Trend in blood lead levels in Taiwanese adults 2005-2017.

This study examined the trend of blood lead levels (BLLs) in Taiwanese adults and analyzed the variations in the BLL between Linkou (northern) and Kaohsiung (southern) hospital branches. Between 2005 and 2017, 3,804 adult participants received blood lead tests at the Linkou (n = 2,674) and Kaohsiung (n = 1,130) branches of Chang Gung Memorial Hospital. The geometric mean of BLL was 2.77 μg/dL. The adult participants from the Kaohsiung branch were not only age older (49.8±14.1 versus 39.4±14.2 years; P<0.001) and male predominant (65.8 versus 41.7%; P<0.001) but also showed a higher BLL (4.45±3.93 versus 2.82±2.42 μg/dL; P<0.001) and lower estimated glomerular filtration rate (87.62±25.94 versus 93.67±23.88; P<0.001) than those from the Linkou branch. Multivariable logistic regression analysis revealed that the Kaohsiung branch [odds ratio (OR): 7.143; 95% confident interval (CI): 5.682-8.929; P<0.001], older age (OR: 1.008; 95% CI: 1.000-1.015; P = 0.043) and reduced estimated glomerular filtration rate (OR: 1.009; 95% CI: 1.004-1.014; P = 0.001) were significant predictors for BLL > 5 μg/dL. Therefore, this study confirmed a continuous decreasing trend in the BLL in Taiwan after banning leaded petrol in 2000.

Introduction

Lead is known for its toxic effects on humans [1]. The symptoms of lead poisoning include impaired cognition, abdominal pain, irritability, impotence, insomnia, a metallic taste in the mouth and headache [2]. In advanced cases, it can lead to seizures, coma and death. The hematologic effects of lead intoxication are reduced hemoglobin synthesis and hemolysis. Lead may cause irreversible neurologic impairment, as well as chronic kidney disease, cardiovascular disease and reproductive damage [2]. Clinical research [3] has also shown that elevated blood lead levels (BLLs) are correlated with all-cause and cardiovascular-cause mortality in the general population.

In Taiwan, the phasing out of lead in petrol started in 1983, and the supply of leaded petrol was banned in 2000. Nevertheless, lead persists in the environment as a toxicant. The diagnosis of lead exposure is primarily based on an elevated BLL. Nevertheless, no level of lead is considered safe. A BLL > 3 μg/dL have been shown to produce reduced cognitive function and maladaptive behavior in many studies [4]. In 2006, Menke et al. [5] investigated U.S. adult participants with a BLL < 10 μg/dL and reported that the hazard ratios for comparisons of participants in the highest tertile of BLL (≥ 3.62 μg/dL) with those in the lowest tertile (< 1.94 μg/dL) were 1.25 for all-cause mortality and 1.55 for cardiovascular mortality. The BLL was correlated with myocardial infarction and stroke mortality, and the correlation was apparent at levels of ≥ 2 μg/dL.

It has been two decades since the banning of leaded petrol in Taiwan. In USA [6], the geometric mean BLL dropped from 12.8 (1976–1980) to 0.82 μg/dL (2015–2016) after control of various lead sources in 1970. For Korea [7], the sale of leaded petrol was prohibited in 1993 and BLLs had decreased to < 2 μg/dL since 2000. However, there is little information regarding longitudinal trend of BLLs in Taiwan. Therefore, the objective of this study was to examine the trend in the BLLs in Taiwanese adult and to analyze the variations in the BLLs between the Southern and Northern parts of Taiwan.

Results

Table 1 outlines the clinical data of the adult participants with an eGFR ≥ 60 mL/min/1.73 m2, stratified by the Linkou or Kaohsiung branch. Between 2005 and 2017, 3,804 adult participants received blood lead tests at the Linkou (n = 2,674) or Kaohsiung (n = 1,130) branch of Chang Gung Memorial Hospital. The mean ages of the adult participants was 42.5 ± 14.9 years, and most were male (58.6%). The geometric mean BLL was 2.77 μg/dL. Adult participants from the Kaohsiung branch were not only age older (49.8 ± 14.1 versus 39.4 ± 14.2 years; P < 0.001) and comprised more males (65.8 versus 41.7%; P < 0.001) but also showed a higher BLL (4.45 ± 3.93 versus 2.82 ± 2.42 μg/dL; P < 0.001) and lower eGFR (87.62 ± 25.94 versus 93.67 ± 23.88; P < 0.001) than adult participants from the Linkou branch. The participants are further divided into 18–60 years of age and 60 years and older. Nevertheless, there was no significant difference in BLL between participants with 18–60 years of age and 60 years and older (3.34 ± 3.15 versus 3.08 ± 2.22 μg/dL; P = 0.064).

Table 1

Clinical data of patients, stratified by Linkou or Kaohsiung branch (n = 3804).

Variable	All adult participants (N = 3804)	Adult participants from Linkou branch of Chang Gung Memorial Hospital (n = 2674)	Adult participants from Kaohsiung branch of Chang Gung Memorial Hospital (n = 1130)	P value
Demographic data
Age (year)	42.5 ± 14.9	39.4 ± 14.2	49.8 ± 14.1	< 0.001***
18–60 years	3269 (86.0)	2383 (89.1)	886 (78.4)	< 0.001***
≥ 60 years	535 (14.0)	291 (10.9)	244 (21.6)	< 0.001***
Male, n (%)	2231 (58.6)	1760 (65.8)	471 (41.7)	< 0.001***
Laboratory data
BLL (μg/dL)	2.77 (2.68–2.86)	2.45 (2.36–2.54)	3.71 (3.48–3.94)	< 0.001***
Serum creatinine level (mg/dL)	0.86 ± 0.19	0.88 ± 0.20	0.83 ± 0.18	< 0.001***
eGFR (mL/min/1.73 m2)	91.88 ± 24.66	93.67 ± 23.88	87.62 ± 25.94	< 0.001***

Note: BLL, blood lead level. eGFR, estimated glomerular filtration rate. BLL was expressed as geometric mean (range). Other parametric variables were presented as the means ± standard deviation, and nonparametric variables were presented as n (%). The geometric mean of BLL was used in this study because it was less affected by extreme values than the arithmetic mean. For comparisons between patient groups, Student’s t test was used for parametric variables and Chi-square or Fisher’s exact tests for nonparametric variables.

***P < 0.001.

A significant continuous decreasing trend in BLLs had been observed (P < 0.001, Fig 1). Moreover, there were rebounds of BLL noted at Kaoshiung branch of Chang Gung Memorial Hospital in 2009, 2013 and 2016. Rebounds of BLL were also noted at Linkou branch in 2009 and 2014. The highest mean BLL of the Kaohsiung branch appeared in 2005 (6.3 ± 4.9 μg/dL) and gradually decreased to 2.3 ± 1.3 μg/dL in 2017. The highest mean BLL of the Linkou branch appeared in 2008–2009 (3.5 ± 1.3 μg/dL) and gradually decreased to 1.8 ± 1.8 μg/dL in 2017.

Fig 1

Trend of blood lead levels (BLLs).

The figure shows the trend of BLLs in Taiwanese adult, 2005–2017. The differences between the means of BLLs in each year were examined by one-way analysis of variance test. A significant continuous decreasing trend (P < 0.001) was noted. Furthermore, the mean BLLs of the Kaohsiung branch were higher than those of the Linkou branch throughout the indicated periods [odds ratio (OR): 7.882; 95% CI (confident interval): 5.682–8.929].

Fig 2A shows the trend of adult participants with a BLL > 5 μg/dL. In total, the percentage of adult participants with a BLL > 5 μg/dL from the Kaohsiung branch was higher than that of the Linkou branch throughout these years. Fig 2B shows the trend of adult participants with a BLL > 10 μg/dL. The percentages of adult participants with a BLL > 10 μg/dL from the Kaohsiung branch were higher than those from the Linkou branch throughout the indicated years.

Fig 2

a. Trend of patients with blood lead levels (BLLs) > 5 μg/dL. b. Trend of patients with blood lead levels (BLLs) > 10 μg/dL.

Multivariable logistic regression analysis (Table 2) revealed that the Kaohsiung branch [odds ratio (OR): 7.882; 95% CI (confident interval): 5.682–8.929], male sex (OR: 1.523; 95% CI: 1.226–1.891) and a reduced eGFR (OR: 0.991; 95% CI: 0.986–0.996) were significant predictors for BLL > 5 μg/dL.

Table 2

Multivariable logistic regression analysis for risk factors associated with BLL > 5 μg/dL (n = 3804).

Variable	Odds ratio	95% Confidence interval	P value
Kaohsiung branch of Chang Gung Memorial Hospital	7.882	5.682–8.929	< 0.001***
Age (per 1 year increase)	0.994	0.986–1.001	0.109
Male sex	1.523	1.226–1.891	< 0.001***
eGFR (per 1 mL/min/1.73 m2 increase)	0.991	0.986–0.996	< 0.001***

Note: BLL, blood lead level. eGFR, estimated glomerular filtration rate.

***P < 0.001.

Discussion

The data in the present study is the first from Taiwan in which both the BLL and eGFR were measured simultaneously, and the analysis confirmed the continuous decreasing trend in the BLL in both branches of Chang Gung Memorial Hospital (Fig 1).

As shown in Table 3 [8-20], a continuous decreasing trend exists in BLLs in Taiwan after banning leaded petrol in 2000. For example, in a study [8] conducted in 1989, Chiang and Chang reported that the mean BLL was higher for traffic policemen than for the control group (24.43 ± 5.31 μg/dL versus 20.14 ± 5.07 μg/dL, respectively; P < 0.01). The result is reasonable because traffic policemen are heavily exposed to vehicle exhaust of leaded petrol. However, another study [18] conducted in 2012 revealed that the mean BLL of children from southern Taiwan was higher than that of children from northern Taiwan (2.79 μg/dL versus 1.95 μg/dL, respectively; P < 0.001). Additionally, the boys’ BLL was higher than the girls’ BLL (2.52 μg/dL versus 2.14 μg/dL, respectively; P < 0.01).

Table 3

Published blood lead prevalence studies from Taiwan.

Study	Year	Sample size	Study group	Serum creatinine level (mg/dL)	eGFR (mL/min/1.73 m2)	BLL (μg/dL)
Chiang and Chang [8]	1989	216	Traffic policemen and students	Not mentioned	Not mentioned	24.43 ± 5.31 (traffic policemen)
						20.14 ± 5.07 (students)
Liou et al. [9]	1994	2919	General population	Not mentioned	Not mentioned	8.29 ± 5.92
Liou et al. [10]	1996	5913	General population	Not mentioned	Not mentioned	8.28 ± 5.39
Liou et al. [11]	1998	8828	General population	Not mentioned	Not mentioned	7.70 ± 5.23
Chu et al. [12]	1998	2803	General population	Not mentioned	Not mentioned	7.3±5.2 (male)
						5.7±3.9 (female)
Wang et al. [13]	2002	934	Primary school children	Not mentioned	Not mentioned	5.50 ± 1.86
Kuo et al. [14]	2006	2565	Aborigines	1.0 ± 0.5 (aborigine)	Not mentioned	5.6 ± 1.4 (aborigine male)
				1.0 ± 0.2 (non-aborigine)		5.4 ± 1.2 (aborigines female)
						5.3 ± 1.2 (non-aborigine male)
						5.3 ± 1.1 (non-aborigines female)
Chang et al. [15]	2006	147	Infertile women	Not mentioned	Not mentioned	3.55 ± 1.39 (infertile women) 2.78 ± 2.05 (fertile women)
Yang et al. [16]	2007	138	Female nursing students	Not mentioned	Not mentioned	2.64 ± 0.84
Wu et al. [17]	2009	154	Immigrant women	Not mentioned	Not mentioned	2.23 ± 1.63 (immigrant women)
						1.63 ± 1.00 (native women)
Huang et al. [18]	2012	238	Children	Not mentioned	Not mentioned	2.79 ± 1.44 (Southern Taiwan)
						1.95 ± 1.51 (Northern Taiwan)
Hwang et al. [19]	2014	934	Preschool children	Not mentioned	Not mentioned	1.84 ± 1.55
Liu et al. [20]	2017	40	General population	Not mentioned	Not mentioned	2.44 ± 0.97
Current study	2021	3804	General population	0.86 ± 0.19	91.88 ± 24.66	2.77 (2.68–2.86)#

Note

#Data was expressed as geometric mean (range).

A significant continuous decreasing trend in BLLs had been observed in our study cohort (Fig 1) and the geometric mean BLL was 2.77 μg/dL (Table 1). Moreover, there were rebounds of BLL noted at Kaoshiung branch of Chang Gung Memorial Hospital in 2009, 2013 and 2016. Rebounds of BLL were also noted at Linkou branch in 2009 and 2014. Nevertheless, there is no clear explanation. In 2016, Tsoi et al. [21] analyzed data from the National Health Nutrition and Examination Survey 1999–2014 and reported a continually decreased trend in BLL in American adult participants. The mean BLLs were 1.65 μg/dL, 1.44 μg/dL, 1.43 μg/dL, 1.29 μg/dL, 1.27 μg/dL, 1.12 μg/dL, 0.97 μg/dL, and 0.84 μg/dL in 1999–2000, 2001–2002, 2003–2004, 2005–2006, 2007–2008, 2009–2010, 2011–2012, and 2013–2014, respectively. In 2002, Becker et al. [22] analyzed data from the German Environmental Survey 1998 and reported that the geometric mean of BLL was 3.1 μg/dL. The SPECT-China Study [23] revealed that the median BLL was 4.40 μg/dL for men and 3.77 μg/dL for women in China. A Spanish study [24] found that the geometric mean BLL was 2.4 μg/dL in adult participants. A meta-analysis from India [25] noted a mean BLL of 7.52 μg/dL in non-occupationally exposed adult participants. The median BLL was 9.9 μg/dl in Congo adult participants [26]. Finally, the geometric means of BLL were 3.25 μg/dL and 6.60 μg/dL in non-occupationally exposed adult participants in Thailand [27] and Singapore [28], respectively.

The major sources of body lead include ingestion (drinking water, paints, food and beverages) and inhalation (factory emission and automobile exhausts) [29]. As shown in Fig 1 and Table 1, adult participants from the Kaohsiung branch showed a higher BLL (4.45±3.93 versus 2.82±2.42 μg/dL; P < 0.001) than those from the Linkou branch. Previous data from our hospital [18] also revealed that the BLLs of pediatric participants from the Kaohsiung branch were higher than those of pediatric participants from the Linkou branch (2.79 versus 1.95 μg/dL, respectively; P < 0.001). This finding is not surprising because Kaohsiung is an international harbor and the heart of heavy and petrochemical industries in Taiwan. Incidents of occupational lead intoxication have been reported in Kaohsiung [30]. However, the Linkou branch is close to Taipei city and serves many residents from the Northern part of Taiwan. Taipei is a modern cosmopolitan city and is the political, economic, educational and cultural center of Taiwan. Therefore, industrial sources of lead are less frequent in Taipei city. Another possible explanation for the higher BLLs in the Kaohsiung branch is particulate matter 2.5 (PM2.5), which is often enriched with lead metal. According to the Environmental Protection Administration of Taiwan, Kaohsiung has been ranked as having the worst PM2.5 air pollution of any city in Taiwan in 2018. A previous study [31] reported that the ambient PM2.5 concentrations in Taipei and Kaohsiung were 23.09 and 48.47 μg/m3, respectively. Apart from air pollution, water pollution is a very serious problem in Kaohsiung city. For example, in July 2000, 100 tons of toxic solvents were dumped into the country’s second longest river, Kaoping, leaving 3 million residents in and around Kaohsiung without drinking water for five days [32]. It is reasonable to assume that the industrial waste could contain toxic metals.

In this study, blood samples were analyzed for lead levels using two different methods, either GF-AAS or ICP-MS. In our hospital, the external quality control or test accuracy of both methods was maintained by participation in Proficiency Testing Program run by the College of American Pathologists. The ICP-MS technique is relatively simpler and faster, spending only one-tenth of the time necessary for GF-AAS with low detection limits [33]. Nevertheless, the accuracy and precision of the method are important in the laboratory analysis of BLLs. In 1997, Zhang et al. [33] demonstrated that the ICP-MS results could be mathematically corrected to be equivalent to the GF-AAS results. Both methods have been widely used as routine analytical methods in the determination of the lead level at our hospital.

Male gender was a significant predictor for BLL > 5 μg/dL (Table 3). This gender difference in BLLs was not surprising given that most past studies also revealed higher values of BLL in males than females. For example, the National Health Nutrition and Examination Survey 1999–2014 [21] indicated that BLLs were consistently higher in males than females. The German Environmental Survey 1998 [22] stated that geometric mean BLL was higher in males (3.6 μg/dL) than females (2.6 μg/dL). Study of general adult population in Iran [34] revealed that the reference values of BLLs for men and women were 16 μg/dL and 15 μg/dL, respectively. It was suggested [35] that the gender difference in BLLs could be explained by the fact that men were engaged in activities that may produce greater and more frequent exposure to lead.

Lead exposure, even at low-level, is associated with renal impairment and incident of chronic kidney disease. In a series of studies, it was demonstrated that environmental exposure to lead was related to progressive renal insufficiency in patients with [36] and without [37-39] diabetes, and chelation therapy may retard renal disease progression in these patients [40]. In a population-based study, researchers from Sweden found that low-level lead exposure was associated with reduced kidney function and incident chronic kidney disease [41]. In another cross-sectional study, researchers from United States [42] reported that low-level lead exposure was associated with lower intelligence quotient and more inattention in children with chronic kidney disease. In a recent systematic review and meta-analysis study [43], it was confirmed that lead exposure was associated with reduced estimated glomerular filtration rate and increased proteinuria risks.

As stated by World Health Organization [1], primary prevention (elimination of exposure to lead at its source) is the single most effective intervention against lead poisoning. In addition to phasing out use of leaded petrol, Taiwan government has been taking many actions to eliminate the use of lead in many products. There is no official guideline for lead exposure in Taiwan, but a whole blood lead test is the test of choice for the diagnosis and monitoring of lead poisoning. It is recommended that BLL should be < 10 μg/dL but < 5 μg/dL for children aged 1–5 years.

Since this study involves retrospective analysis of existing data, only adult participants who visited Chang Gung Memorial Hospital between 2005 and 2017 were recruited for analysis. Therefore, this study is clearly limited by the lacking of standard sampling protocol to select study participants. Furthermore, the study participants were recruited from hospital, which might differ from general population. Further epidemiologic studies with standard sampling protocol targeting at recruiting participants from general population are warranted.

Conclusion

In summary, the geometric mean BLL for Taiwanese adult was 2.77 μg/dL. Adult participants from the Kaohsiung branch were not only age older and male predominant but also showed higher BLLs and had lower estimated glomerular filtration rate than adult participants from the Linkou branch. The Kaohsiung branch, male sex and a reduced estimated glomerular filtration rate were risk factors associated with a BLL > 5 μg/dL. Finally, this study confirmed a continuous decreasing trend in BLLs in Taiwan after the banning of leaded petrol in 2000.

Materials and methods

Ethical statement

This observational study adhered to the guidelines of Declaration of Helsinki and was approved by the Medical Ethics Committee of Chang Gung Memorial Hospital. Since this study included a retrospective analysis of existing data, Institutional Review Board approval was acquired without specific informed consent from the patients. The Institutional Review Board of the Chang Gung Memorial Hospital had waived the need for consent, and the Institutional Review Board number was 201701031A3.

Participants

This study was conducted in adult participants who visited the Linkou or Kaohsiung branches of Chang Gung Memorial Hospital and received their blood lead tests between 2005 and 2017. Since these patients also received blood test for creatinine, the estimated glomerular filtration rate was a calculation based on a serum creatinine test. The blood lead level was only measured once per subject. Chang Gung Memorial Hospital offers the largest health care services in Taiwan, comprising a network of several hospital branches located in Linkou, Taipei, Taoyuan, Keelung, Yunlin, Chiayi, and Kaohsiung (Web address: http://www.chang-gung.com/en/about.aspx?id=11&bid=1). The Linkou and Kaohsiung branches are the two main branches. The Linkou branch primarily serves patients from the northern part of Taiwan, while the Kaohsiung branch primarily serves patients from the southern part of Taiwan.

Inclusion and exclusion criteria

All the adult participants with an estimated glomerular filtration rate ≥ 60 mL/min/1.73 m2 and who received blood lead tests between 2005 and 2017 were recruited for this study. Adult participants with an estimated glomerular filtration rate < 60 mL/min/1.73 m2 or participants aged younger than 18 years were excluded from the analysis. Theoretically, lead is concentrated in the kidney after body absorption and is then excreted in urine [44]. Patients with chronic kidney disease might show elevated BLLs due to decreased urinary excretion of lead. Therefore, participants with estimated glomerular filtration rate < 60 mL/min/1.73 m2 were excluded because this could confound the analyses.

Blood sample collection and serum biochemistry

Whole blood samples from each participant were collected in metal-free tubes (Vacutainer; BD 368381; Becton-Dickson, Franklin Lakes, NJ, USA). The BLLs were measured using either graphite furnace atomic absorption spectrometry (GFAAS) (PinAAcle 900T; PerkinElmer, Waltham, Massachusetts, USA) or inductively coupled plasma mass spectrometry (ELAN DRC-e; PerkinElmer, Waltham, Massachusetts, USA). The serum creatinine levels were measured using an automated biochemical analyzer (LABOSPECT 008; Hitachi, Tokyo, Japan).

Graphite furnace atomic absorption spectrophotometry (GF-AAS)

Whole blood specimens (200 μL) were diluted (1 + 4) with a matrix modifier solution. All the standards were purchased from High-Purity Standards, traceable to the NIST (South Carolina, USA). Calibration was performed using a reagent blank with five calibration standards. Calibration curves for lead had an R ≥ 0.995 and a blank absorbance < 0.005. The recovery rate for lead was within 90%–110%. The limit of quantification was 1.0 μg/dL. Quality controls were analyzed at the start and end of each analytical run, and once per level again after every 10 samples. Test precision was monitored using a coefficient of variation of less than 5% at each level of control. The test accuracy was validated regularly by the College of American Pathologist proficiency testing.

Inductively coupled plasma mass spectrometry (ICP-MS)

Whole blood specimens (250 μL) were diluted (1 + 20) with 1.5% nitric acid (JT Baker, New Jersey, USA) solution containing yttrium as an internal standard. All the standards were purchased from High-Purity Standards (South Carolina, USA). Calibration was performed using a reagent blank and six calibration standards in the internal standard diluent solution. Calibration curves for lead had an R ≥ 0.995. The recovery rate for lead was 90%~110%. The limit of quantification was 0.7 μg/dL. Quality controls were analyzed at the start and end of each analytical run, and once per level again after every 10 samples. Test precision was monitored using a coefficient of variation less than 5% at each level of control. The test accuracy was validated regularly by the College of American Pathologist proficiency testing.

Statistical analysis

Statistical analysis was performed using PASW software (version 18.0; SPSS Inc., Chicago, IL, USA). Parametric variables were expressed as the means and standard deviations, and nonparametric variables were expressed as numbers with percentages in brackets. All the data were tested for normality of distribution and equality of standard deviations before analysis. The Quantile-quantile plot and Kolmogorov-Smirnov test were used to check the normality of distribution. The Levene test was used to check the equality of variance. For comparisons between patient groups, we used Student’s t test for parametric variables and Chi-square or Fisher’s exact tests for nonparametric variables. The differences between the means of BLLs in each year were examined by one-way analysis of variance test. A multivariable binary logistic regression analysis was performed to analyze potential predictors for BLL > 5 μg/dL. The variables included age, sex, estimated glomerular filtration rate and branch of Chang Gung Memorial Hospital. A P value < 0.05 was considered statistically significant.

17 Sep 2021

PONE-D-21-24583

Trend in blood lead levels in Taiwanese adults 2005 - 2017

PLOS ONE

Dear Dr. Tzung-Hai Yen,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

Please give a point to point reply of the reviewer comments in your revised manuscript.

Please submit your revised manuscript by 10 Sep. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

Please include the following items when submitting your revised manuscript:

A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.

A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'.

An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter.

If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: http://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols. Additionally, PLOS ONE offers an option for publishing peer-reviewed Lab Protocol articles, which describe protocols hosted on protocols.io. Read more information on sharing protocols at https://plos.org/protocols?utm_medium=editorial-email&utm_source=authorletters&utm_campaign=protocols.

We look forward to receiving your revised manuscript.

Kind regards,

Purvi Purohit

Academic Editor

PLOS ONE

Journal Requirements:

When submitting your revision, we need you to address these additional requirements.

1. Please ensure that your manuscript meets PLOS ONE's style requirements, including those for file naming. The PLOS ONE style templates can be found at

https://journals.plos.org/plosone/s/file?id=wjVg/PLOSOne_formatting_sample_main_body.pdf and

https://journals.plos.org/plosone/s/file?id=ba62/PLOSOne_formatting_sample_title_authors_affiliations.pdf

2. In your Data Availability statement, you have not specified where the minimal data set underlying the results described in your manuscript can be found. PLOS defines a study's minimal data set as the underlying data used to reach the conclusions drawn in the manuscript and any additional data required to replicate the reported study findings in their entirety. All PLOS journals require that the minimal data set be made fully available. For more information about our data policy, please see http://journals.plos.org/plosone/s/data-availability.

"Upon re-submitting your revised manuscript, please upload your study’s minimal underlying data set as either Supporting Information files or to a stable, public repository and include the relevant URLs, DOIs, or accession numbers within your revised cover letter. For a list of acceptable repositories, please see http://journals.plos.org/plosone/s/data-availability#loc-recommended-repositories. Any potentially identifying patient information must be fully anonymized.

Important: If there are ethical or legal restrictions to sharing your data publicly, please explain these restrictions in detail. Please see our guidelines for more information on what we consider unacceptable restrictions to publicly sharing data: http://journals.plos.org/plosone/s/data-availability#loc-unacceptable-data-access-restrictions. Note that it is not acceptable for the authors to be the sole named individuals responsible for ensuring data access.

We will update your Data Availability statement to reflect the information you provide in your cover letter.

3. Please review your reference list to ensure that it is complete and correct. If you have cited papers that have been retracted, please include the rationale for doing so in the manuscript text, or remove these references and replace them with relevant current references. Any changes to the reference list should be mentioned in the rebuttal letter that accompanies your revised manuscript. If you need to cite a retracted article, indicate the article’s retracted status in the References list and also include a citation and full reference for the retraction notice.

Additional Editor Comments:

The authors are required to do some minor revisions throughout the manuscript as pointed out by the two reviewers.

Please ensure that point to point explanation of the reviewer comments is made while submitting the revised manuscript.

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: Yes

**********

2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: Yes

**********

3. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: No

Reviewer #2: No

**********

4. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

**********

5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: The authors here present a trend in blood lead levels in Taiwanese adults. The objectives, methods, and summary of the results have been described succinctly with relevant statistics. However, minor revisions need to be incorporated.

General:

1. There are syntax and punctuation issues throughout the document, which detracts the readability of the text. I have highlighted a few, but a thorough proofreading of the manuscript would be beneficial. Some of the longer sentences could also benefit from rephrasing. Further, a period should go after "et al" regardless of where it is mentioned in the sentence.

2. It would be helpful for the readers if the statistics/tests performed for the comparisons in the tables and figures are also mentioned in the table footnotes/figure legends.

Abstract:

The last sentence is a repetition of the findings already mentioned, and hence, can be removed.

Introduction:,.

Line 66: remove ‘because’

Results:

Line 85: age

Table 1 depicts the demographic and laboratory data. In the demographic data, the participants are further divided into 18-60 years of age and 60 years and older.

(1) Both groups seem to have included the participants who are 60 years of age. Based on the data shown in Figure 2a and 2b, I presume the first group is 18-59 years and the second group would be 60 years and older. Kindly rectify.

(2) In Table 1, the BLL should also be compared between these two age groups separately.

(3) The BLL is reported as geometric mean and range in the tables 1 and 3 but as geometric mean and SD (this is geometric SD, I presume; kindly clarify) elsewhere in the text. The authors should address the reason for this or keep the reporting uniform throughout.

Line 97: The authors mention a significant decreasing trend of BLL. Statistical details of how the differences between both the trends were analyzed can be included in the figure legend (Figure 1).

Lines 98-99, 145-156: BLL rebounds are noted in Linkou branch in 2009 and 2016. However, Figure 1 seems to depict the same for Kaosiung branch. Kindly confirm or address.

Line 135: Fix the citation.

Discussion:

Since eGFR was a significant predictor for blood lead levels, a brief section can be added discussing the relation between lead exposure and kidney function citing relevant literature.

Lines 155, 157: same word with and without hyphen; make them uniform.

Line 198: “by the fact..”

Line 210: “by the lack of a standard sampling protocol..”

Methods:

In the statistics section, mention the tests used for checking the normality of distribution and equality of variance.

Reviewer #2: Manuscript is technically sound, and the data supports the conclusions. The statistical analysis has been performed appropriately.The data points behind means, medians and variance measures should be made available.

1. In introduction section: Please elaborate on "BLL < 10 μg/dL showed higher cardiovascular mortality than those with BLLs >3.61 μg/dL and <10 μg/dL"...

2. In results section"Figure 1 Trend of blood lead levels (BLLs) in Taiwanese adult, 2005 -2017" should be rephrased to Figure 1 shows the trend of blood lead levels (BLLs) in Taiwanese adult, 2005 -2017.... and CI (confident interval): 5.682 – 8.929]"...its confidence interval

3. In discussion section the sentence " It is recommended that BLL should be < 10 µg/dL but < 5 µg/dL for children aged 1–5 years" should be elaborated. eGFR is the novelty of the paper and hence BLL and eGFR should be discussed in detail.

4. In methodology, inclusion exclusion criteria "Lead is concentrated in the kidney after body absorption and is then excreted in urine. Patients with chronic kidney disease might show elevated BLLs due to decreased urinary excretion"....this is a generalized statement and support the statement with adequate references.

**********

6. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: No

Reviewer #2: No

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.]

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org. Please note that Supporting Information files do not need this step.

31 Oct 2021

Reviewer #1: The authors here present a trend in blood lead levels in Taiwanese adults. The objectives, methods, and summary of the results have been described succinctly with relevant statistics. However, minor revisions need to be incorporated.

General:

1. There are syntax and punctuation issues throughout the document, which detracts the readability of the text. I have highlighted a few, but a thorough proofreading of the manuscript would be beneficial. Some of the longer sentences could also benefit from rephrasing. Further, a period should go after "et al" regardless of where it is mentioned in the sentence.

Response: Thank you for the comments. This manuscript has been sent to AJE for English grammar editing prior to first submission. Please advise us again if we miss out anything.

2. It would be helpful for the readers if the statistics/tests performed for the comparisons in the tables and figures are also mentioned in the table footnotes/figure legends.

Response: Thank you for the comment. The information has been included in the table footnotes/figure legends.

Abstract:

The last sentence is a repetition of the findings already mentioned, and hence, can be removed.

Response: Thank you for the comment. The sentence has been removed.

Introduction:,.

Line 66: remove ‘because’

Response: Thank you for the comment. The word has been removed.

Results:

Line 85: age

Response: Thank you for the comment. The word has been included.

Table 1 depicts the demographic and laboratory data. In the demographic data, the participants are further divided into 18-60 years of age and 60 years and older.

(1) Both groups seem to have included the participants who are 60 years of age. Based on the data shown in Figure 2a and 2b, I presume the first group is 18-59 years and the second group would be 60 years and older. Kindly rectify.

Response: Thank you for the comment. The paragraph has been revised.

The participants are further divided into 18 - 60 years of age and 60 years and older. Nevertheless, there was no significant difference in BLL between participants with 18 - 60 years of age and 60 years and older (3.34 ± 3.15 versus 3.08 ± 2.22 µg/dL; P = 0.064).

(2) In Table 1, the BLL should also be compared between these two age groups separately.

Response: Thank you for the comment. The paragraph has been revised.

The participants are further divided into 18-60 years of age and 60 years and older. Nevertheless, there was no significant difference in BLL between participants with 18 - 60 years of age and 60 years and older (3.34 ± 3.15 versus 3.08 ± 2.22 µg/dL; P = 0.064).

(3) The BLL is reported as geometric mean and range in the tables 1 and 3 but as geometric mean and SD (this is geometric SD, I presume; kindly clarify) elsewhere in the text. The authors should address the reason for this or keep the reporting uniform throughout.

Response: Thank you for the comment. The footnote of Table 1 and 3 have been revised.

BLL was expressed as geometric mean (range). Other parametric variables were presented as the means ± standard deviation, and nonparametric variables were presented as n (%). The geometric mean of BLL was used in this study because it was less affected by extreme values than the arithmetic mean.

Line 97: The authors mention a significant decreasing trend of BLL. Statistical details of how the differences between both the trends were analyzed can be included in the figure legend (Figure 1).

Response: Thank you for the comment. The figure legend has been revised according to comments of both reviewers.

Figure 1 Trend of blood lead levels (BLLs). The figure shows the trend of BLLs in Taiwanese adult, 2005 -2017. The differences between the means of BLLs in each year were examined by one-way analysis of variance test. A significant continuous decreasing trend (P < 0.001) was noted. Furthermore, the mean BLLs of the Kaohsiung branch were higher than those of the Linkou branch throughout the indicated periods [odds ratio (OR): 7.882; 95% CI (confident interval): 5.682 – 8.929].

Lines 98-99, 145-156: BLL rebounds are noted in Linkou branch in 2009 and 2016. However, Figure 1 seems to depict the same for Kaosiung branch. Kindly confirm or address.

Response: Thank you for the comment. The sentences have been revised.

A significant continuous decreasing trend in BLLs had been observed (P < 0.001, Figure 1). Moreover, there were rebounds of BLL noted at Kaoshiung branch of Chang Gung Memorial Hospital in 2009, 2013 and 2016. Rebounds of BLL were also noted at Linkou branch in 2009 and 2014.

Line 135: Fix the citation.

Response: Thank you for reminding us. The citation has been revised.

Discussion:

Since eGFR was a significant predictor for blood lead levels, a brief section can be added discussing the relation between lead exposure and kidney function citing relevant literature.

Response: Thank you for the comment. A new paragraph has been added in Discussion section.

Lead exposure, even at low-level, is associated with renal impairment and incident of chronic kidney disease. In a series of studies, it was demonstrated that environmental exposure to lead was related to progressive renal insufficiency in patients with [36] and without [37-39] diabetes, and chelation therapy may retard renal disease progression in these patients [40]. In a population-based study, researchers from Sweden found that low-level lead exposure was associated with reduced kidney function and incident chronic kidney disease [41]. In another cross-sectional study, researchers from United States [42] reported that low-level lead exposure was associated with lower intelligence quotient and more inattention in children with chronic kidney disease. In a recent systematic review and meta-analysis study [43], it was confirmed that lead exposure was associated with reduced estimated glomerular filtration rate and increased proteinuria risks.

Lines 155, 157: same word with and without hyphen; make them uniform.

Response: Thank you for the comment. The word has been revised.

Line 198: “by the fact..”

Response: Thank you for the comment. The sentence has been revised.

Line 210: “by the lack of a standard sampling protocol..”

Response: Thank you for the comment. The sentence has been revised.

Methods:

In the statistics section, mention the tests used for checking the normality of distribution and equality of variance.

Response: Thank you for the comment. The analytical method has been provided.

The Quantile-quantile plot and Kolmogorov-Smirnov test were used to check the normality of distribution. The Levene test was used to check the equality of variance.

Reviewer #2: Manuscript is technically sound, and the data supports the conclusions. The statistical analysis has been performed appropriately. The data points behind means, medians and variance measures should be made available.

1. In introduction section: Please elaborate on "BLL < 10 μg/dL showed higher cardiovascular mortality than those with BLLs >3.61 μg/dL and <10 μg/dL"...

Response: Thank you for the comment. The study has been elaborated.

In 2006, Menke et al [5] investigated U.S. adult participants with a BLL < 10 μg/dL and reported that the hazard ratios for comparisons of participants in the highest tertile of BLL (≥ 3.62 μg/dL) with those in the lowest tertile (< 1.94 μg/dL) were 1.25 for all-cause mortality and 1.55 for cardiovascular mortality. The BLL was strongly correlated with myocardial infarction and stroke mortality, and the correlation was apparent at levels of ≥ 2 μg/dL.

2. In results section "Figure 1 Trend of blood lead levels (BLLs) in Taiwanese adult, 2005 -2017" should be rephrased to Figure 1 shows the trend of blood lead levels (BLLs) in Taiwanese adult, 2005 -2017.... and CI (confident interval): 5.682 – 8.929]"...its confidence interval

Response: Thank you for the comment. The figure legend has been revised according to comments of both reviewers.

Figure 1 Trend of blood lead levels (BLLs). The figure shows the trend of BLLs in Taiwanese adult, 2005 -2017. The differences between the means of BLLs in each year were examined by one-way analysis of variance test. A significant continuous decreasing trend (P < 0.001) was noted. Furthermore, the mean BLLs of the Kaohsiung branch were higher than those of the Linkou branch throughout the indicated periods [odds ratio (OR): 7.882; 95% CI (confident interval): 5.682 – 8.929].

3. In discussion section the sentence " It is recommended that BLL should be < 10 µg/dL but < 5 µg/dL for children aged 1–5 years" should be elaborated. eGFR is the novelty of the paper and hence BLL and eGFR should be discussed in detail.

Response: Thank you for the comment. A new paragraph has been added in Discussion section.

Lead exposure, even at low-level, is associated with renal impairment and incident of chronic kidney disease. In a series of studies, it was demonstrated that environmental exposure to lead was related to progressive renal insufficiency in patients with [36] and without [37-39] diabetes, and chelation therapy may retard renal disease progression in these patients [40]. In a population-based study, researchers from Sweden found that low-level lead exposure was associated with reduced kidney function and incident chronic kidney disease [41]. In another cross-sectional study, researchers from United States [42] reported that low-level lead exposure was associated with lower intelligence quotient and more inattention in children with chronic kidney disease. In a recent systematic review and meta-analysis study [43], it was confirmed that lead exposure was associated with reduced estimated glomerular filtration rate and increased proteinuria risks.

4. In methodology, inclusion exclusion criteria "Lead is concentrated in the kidney after body absorption and is then excreted in urine. Patients with chronic kidney disease might show elevated BLLs due to decreased urinary excretion"....this is a generalized statement and support the statement with adequate references.

Response: Thank you for the comment. The statement has been referenced.

Submitted filename: Response to reviewers.doc

Click here for additional data file.

17 Nov 2021

Trend in blood lead levels in Taiwanese adults 2005 - 2017

PONE-D-21-24583R1

Dear Dr. Tzung-Hai Yen

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication.

An invoice for payment will follow shortly after the formal acceptance. To ensure an efficient process, please log into Editorial Manager at http://www.editorialmanager.com/pone/, click the 'Update My Information' link at the top of the page, and double check that your user information is up-to-date. If you have any billing related questions, please contact our Author Billing department directly at authorbilling@plos.org.

If your institution or institutions have a press office, please notify them about your upcoming paper to help maximize its impact. If they’ll be preparing press materials, please inform our press team as soon as possible -- no later than 48 hours after receiving the formal acceptance. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact onepress@plos.org.

Kind regards,

Purvi Purohit

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

The authors have responded appropriately to all the queries raised by the reviewers. The manuscript has been revised and the manuscript is now acceptable for publication.

22 Nov 2021

PONE-D-21-24583R1

Trend in blood lead levels in Taiwanese adults 2005 - 2017

Dear Dr. Yen:

I'm pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now with our production department.

If your institution or institutions have a press office, please let them know about your upcoming paper now to help maximize its impact. If they'll be preparing press materials, please inform our press team within the next 48 hours. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information please contact onepress@plos.org.

If we can help with anything else, please email us at plosone@plos.org.

Thank you for submitting your work to PLOS ONE and supporting open access.

Kind regards,

PLOS ONE Editorial Office Staff

on behalf of

Dr. Purvi Purohit

Academic Editor

PLOS ONE