Biomonitoring of mercury and lead in vulnerable communities of the Colombian Caribbean: Exposure and impacts on human health

Abstract

Heavy metal pollution is a major public health concern. Mercury (Hg) and Lead (Pb) are widespread heavy metals, recognized as global contaminants. These harmful chemicals are normally present in nature, but different anthropogenic activities have increased biota and human exposure. Among these activities, Hg is used in gold mining and Pb in fishing tools manufacture. This is critical at developing countries, where those represent a significant environmental risk for the population, especially for vulnerable communities. In Colombia, Hg is highly used in gold mining activities, most carried out as the only economic activity for many families. The lack of good practices and technological tools allows Hg to reach nearby ecosystems, where it can be bioaccumulated in the food web and human. Therefore, high Hg concentrations have been found in carnivorous fish and humans. In this sense, this study was carried out to evaluate total Hg (T-Hg) concentrations in human hair, fish, soil, and air from two major gold-mining districts (GMDs), the Mojana region and the Middle Magdalena in the department of Bolivar, Colombia. Total Hg (T-Hg) concentrations were evaluated at two major GMDs, at the department of Bolivar. Total Hg was analyzed using a direct Hg analyzer. Average T-Hg level in hair samples was 3.07 ± 0.14 μg/g (range 0.15–25.1 μg/g; median 2.02 μg/g). The highest Hg level was observed in Mojana GMD, specifically at Achi-La Raya (9.2 ± 0.6 μg/g) and the lowest in Morales, at the Middle Magdalena GMD (1.50 ± 0.16 μg/g). Hair T-Hg values exceeded the U.S. Environmental Protection Agency (USEPA) reference level of 1.0 μg/g. Total Hg fish concentrations were evaluated in several fish species, including, Caquetaia kraussii, Sorubim cuspicaudus, 8 Plagioscion surinamensis, Trachelyopterus insignis, Prochilodus magdalenae and Pseudoplatystoma magdaleniatum. The highest average T-Hg fish concentration was observed in Caquetaia kraussii (0.37 ± 0.10 μg/g), whereas the lowest (0.03 ± 0.01 μg/g) was reported in Prochilodus magdalenae. Human health risk assessment of Hg exposure, based on fish consumption, suggested that, with the exception of P. magdalenae, all economically significant fish species are potentially harmful for the communities. Soil Hg levels in amalgam burning facilities were extremely high, and Hg in the air around mining areas and gold-processing shops exceeded international guidelines. Mercury is not the only chemical threat in vulnerable populations. Currently, Pb is particularly influential as a pollutant in many fishing communities. Children are highly vulnerable to Pb poisoning because this metal has the potential to exert deleterious effects, in particular at the nervous system, causing cognitive deficits, behavioral problems, on the other hand, anemia, infertility, hepatic effects, hearing impairment, immune-related diseases, decreased physical growth, and hypertension, among others. Thus, in this study Blood lead levels (BLL) were assessed in children from two fishing communities in Northern Colombia, Loma de Arena and Tierrabomba, evaluating their association with morphometric parameters, markers of hematological status, liver function, and mRNA expression of genes related to Pb toxicity. A total of 198 blood samples were collected from participants aged 5–16 years old. The mean (± standard error) BLL for the studied sample was 3.6 ± 0.3 μg/dL. The participants of Loma de Arena and Tierrabomba presented BLL of 3.9 ± 0.5 and 2.9 ± 0.3 μg/dL, respectively. 9 Children born preterm had greater BLL than those born at full term. Boys had greater BLL than girls, which also occurred for participants between 12 and 16 years old, compared with those aged 5–11 years old. The BLL were negatively correlated with body mass index in children from Loma de Arena, but an opposite behavior was observed for Tierrabomba. In Loma de Arena, the mRNA expression of interferon gamma, a pro-inflammatory cytokine, increased with the BLL, while that of δ-aminolevulinic acid dehydrogenase, a sensor for Pb poisoning, decreased. In Tierrabomba, gene expression did not change with BLL. In conclusion, these results show that in fishing communities lead exposure promotes different health impacts depending on age, sex, and other site-specific factors. In any case, appropriate educational and intervention programs should be carried out to minimize Pb exposure in children.