Biomarkers of renal effects in children and adults with low environmental exposure to heavy metals.

The health effects of chronic exposure to heavy metals such as lead, cadmium, and mercury are widely documented, yet few data exist about the renal impact of low environmental exposure to these metals, particularly in children. The aim of this study was to assess renal parameters in children and adults living in an environment known for its past heavy metal contamination around two nonferrous smelters in northern France (Noyelles-Godault and Auby) and to compare their results with age and gender-matched controls living in neighboring municipalities with unpolluted soil (total: 400 children, 600 adults, sex ratio = 1). The integrity of renal function was assessed by measuring the urinary excretion levels of total protein, albumin, transferrin, beta(2)-microglobulin, retinol-binding protein, brush border antigen, and the enzyme N-acetyl-beta-D-glucosaminidase (NAG). The mean blood concentrations of lead (Pb-B, children </=42.2 micro/L, adults </=71.3. micro/L) and of cadmium (Cd-B, children </=0.52 microg/L, adults 0.86 microg/L) were all relatively low, indicating a low uptake of these heavy metals from the environment despite relatively high levels in soil (between 100 and 1700 ppm for lead and 0.7 to 233 ppm for cadmium). Pb-B levels were, however, significantly increased in boys, girls, and women--but not men--living in the polluted area. Boys, men, and women living in the polluted area had also on average higher Cd-B levels. The concentrations of mercury in urine (Hg-U) were by contrast similar in control and exposed groups. None of the renal parameters studied showed a significant difference between control and exposed groups. The influence of heavy metals on renal parameters was further assessed by stepwise multiple regression, testing Pb-B, Cd-B, Hg-U, age, gender, body mass index (BMI), urinary creatinine levels, and area of residence as predictors in both children and adults, including first-order metal interaction terms, smoking habits, and alcohol consumption in adults. The only positive correlation was found between the urinary excretion of NAG activity (standardized for BMI and urinary creatinine) and Cd-B levels when taking the whole children population, indicating that even low cadmium burdens may produce subtle effects on the proximal tubule in children, although deleterious consequences are unlikely should exposure not increase. However, in the absence of other positive findings even after studying the smaller subgroups with higher levels of heavy metals, these results are clearly indicative of the minimal renal impact of living around nonferrous smelters that are currently complying with pollution regulations, even when soil contamination is still high.