Ecological and human health risk from exposure to contaminated sediments in a tropical river impacted by gold mining in Colombia.

Despite being one of the most important tropical biomes in the world, the Atrato River basin has experienced a critical ecological deterioration due to gold mining, posing a significant threat to wildlife and human health. In this study, we measured the concentrations of mercury (Hg) and arsenic (As) in sediments at various swamps within the basin. Classical indices were employed to assess the associated ecological and human health risks linked to exposure to these elements. The concentrations of Hg and As in the sediments ranged between 0.09 and 0.23 mg/kg and 0.59-2.68 mg/kg, respectively. The highest Hg values were found at upstream stations impacted by gold mining activities. For As, the highest levels were found near river mouth (except for station B), where agricultural practices are taken place. The contamination factor (CF) indicated that most of the sediments exhibited moderate contamination levels of Hg and As, depending on the specific sampling area. Conversely, the pollution load index (PLI) suggested a contamination level ranging from basic to moderate, with the exception of station B, which showed a progressive deterioration of the site. The geoaccumulation index (Igeo) indicated that the sediments were moderately contaminated with Hg, while showing signs of increasing contamination for As. According to the criteria for limiting effect concentrations (TEC), Hg concentrations exceeded the TEC at stations B and C, indicating a potential toxic risk to aquatic biota. A moderate potential ecological risk (PERI) was detected at downstream stations (D and E), and a high risk was detected at upstream stations (A, B and C). The hazard index (HI), used for non-carcinogenic risk assessment, suggested a risk of adverse effects on the population, particularly in children, with HI values exceeding 1. However, all lifetime cancer risk (TLCR) values fell within the acceptable range (1 × 10-6 to 1 × 10-4), indicating a negligible risk. Oral ingestion and inhalation were identified as the two primary routes of concern. This study serves as a valuable reference for risk assessment regarding exposures to environmental matrices that may not pose an immediate risk to human health.

Toxic metal(loids) levels in the aquatic environment and nuclear alterations in fish in a tropical river impacted by gold mining.

The Atrato River basin was protected by Colombian law due to anthropogenic impacts, mainly from illegal gold mining, which triggered a critical environmental health problem. In this study we quantified mercury (Hg), methylmercury (MeHg) and arsenic (As) concentrations in aquatic environmental matrices, and explored for the first-time nuclear degenerations in fish from the Atrato River. The median concentrations (µg/kg) for T-Hg, MeHg and As in fish were 195.0, 175.5, and 30.0; in sediments (µg/kg) 165.5, 13.8 and 3.1; and in water (ng/L), 154.7 for T-Hg and 2.1 for As. A 38% and 10% of the fish exceeded the WHO limit for the protection of populations at risk (200 µg Hg/kg) and for human consumption (500 µg Hg/kg); while As concentrations were below the international standard (1000 µg/kg) in all fish. The percentage of MeHg was 89.7% and the highest accumulation was observed in carnivorous fish (336.3 ± 245.6 µg/kg, p < 0.05) of high consumption, indicating risk to human health. In water, T-Hg concentrations exceeded the threshold effect value of 12 ng/L, whereas As concentrations were below the threshold of 10,000 ng/L, established by USEPA. On the contrary, 33% of the sediments exceeded the quality standard of 200 µg/kg for Hg. We found that Prochilodus magdalenae was the species with the highest susceptibility to nuclear alterations in its order, nuclear bud (CNB, 3.7 ± 5.4%), micronuclei (MN, 1.6 ± 2.5%) and binucleated cells (BC, 1.6 ± 2.3%). These results indicate that the species appears to be a good predictor of genotoxicity in the Atrato River. Fulton's condition factor (K) indicated that 31.7% of the fishes had poor growth condition, suggesting that the Atrato River basin needs to be monitored and restored in accordance with the agreements reached in the Minamata Convention on Mercury.

Drivers of biomagnification of Hg, As and Se in aquatic food webs: A review.

Biomagnification of trace elements is increasingly evident in aquatic ecosystems. In this review we investigate the drivers of biomagnification of mercury (Hg), arsenic (As) and selenium (Se) in aquatic food webs. Despite Hg, As and Se biomagnify in food webs, the biomagnification potential of Hg is much higher than that of As and Se. The slope of trophic increase of Hg is consistent between temperate (0.20), tropical (0.22) and Arctic (0.22) ecosystems. Se exerts a mitigating role against Hg toxicity but desired maximum and minimum concentrations are unknown. Environmental (e.g. latitude, temperature and physicochemical characteristics) and ecological factors (e.g. trophic structure composition and food zone) can substantially influence the biomagnification process these metal (oids). Besides the level of bioaccumulated concentration, biomagnification depends on the biology, ecology and physiology of the organisms that play a key role in this process. However, it may be necessary to determine strictly biological, physiological and environmental factors that could modulate the concentrations of As and Se in particular. The information presented here should provide clues for research that include under-researched variables. Finally, we suggest that biomagnification be incorporated into environmental management policies, mainly in risk assessment, monitoring and environmental protection methods.