Spatial distribution and evaluation of environmental pollution by mercury in the Mojana region, Colombia

Objective. To evaluate the distribution of total mercury (THg) in surface sediments, fish, hair, rice plants, and macrophytes, as well as the geoaccumulation index by THg in sediments and the risk potential for fish consumption in different municipalities affected by gold mining activities that have developed around in the Mojana region, Colombia. Materials and methods. The THg concentration was determined by thermal decomposition, using a direct DMA-80 mercury analyzer. Results. On average, the concentrations of THg in fish was 0.223±0.027 μg/g. Of the total fish samples, 11.6% exceeded the permissible limit established by the World Health Organization (0.5 μg/g), being 4.2% for non-carnivorous species and 7.4% for carnivorous species. Of the fish species, 76.9% showed risk index (HI) values greater than 1. The Geoaccumulation Index (Igeo) in sediments shows a contamination degree from non-polluted to moderate pollution for the different sampling stations. Hair THg concentrations ranged between 0.17- 8.8 μg/g. Of the population, 47% exceeds the permissible limit established as a reference by the USEPA (1 μg/g). THg concentrations in macrophytes (Eichhornia crassipes) and rice crop plants were higher in sampling stations that receive water currents that carry contaminating loads from mining areas, a similar trend presented for sediments and fish. Conclusions. Mining activities have generated a process of gradual contamination by Hg in the food chain and currently levels in fish, rice and hair represent a serious concern for human health.