Mercury contamination in the vicinity of a chlor-alkali plant and potential risks to local population.

A mercury-cell chlor-alkali plant operated in Estarreja (North-western Portugal) for 50 years causing widespread environmental contamination. Although production by this process ceased in 2002, mercury contamination from the plant remains significant. The main objective of this study was to investigate mercury impact on the nearby environment and potential risks to local population. To assess the level of contamination soil samples were collected from agricultural fields in the vicinity of the plant, extending the study by taking samples of the predominant vegetation suitable for animal and human consumption, water samples, and fish species from a nearby coastal lagoon, to gain a preliminary insight into the potential for contamination of the terrestrial and aquatic food web. To determine population exposure to mercury, hair samples were collected from local residents. Total mercury concentration in the 0-15 cm layer of soil was found to be highly variable, ranging between 0.010 and 91 mg kg(-1), although mercury contamination of soils was found to be restricted to a confined area. Lolium perenne roots contained between 0.0070 and 2.0 mg kg(-1), and there is evidence that root systems uptake mercury from the soil. Levels of mercury in the aerial parts of plants ranged between 0.018 and 0.98 mg kg(-1). It appears that plants with higher mercury concentration in soils and roots also display higher mercury concentration in leaves. Total mercury concentration in water samples ranged between 12 and 846 ng L(-1), all samples presenting concentrations below the maximum level allowable for drinking water defined in the Portuguese law (1.0 microg L(-1)). Mercury levels in fish samples were below the maximum limit defined in the Portuguese law (0.5 mg kg(-1)), ranging from 0.0040 to 0.24 mg kg(-1). Vegetables collected presented maximum mercury concentration of 0.17 mg kg(-1). In general, food is not contaminated and should not be responsible for major human exposure to the metal. Mercury determined in human hair samples (0.090-4.2 mg kg(-1); mean 1.5 mg kg(-1)) can be considered within normal limits, according to WHO guidelines suggesting that it is not affecting the local population. Despite being subject to decades of mercury emissions, nowadays this pollutant is only found in limited small areas and must not constitute a risk for human health, should these areas be restricted and monitored. Considering the present data, it appears that the population from Estarreja is currently not being affected by mercury levels that still remain in the environment.