STRONG GEOLOGICAL CONTROLS AND ORIGIN EVIDENT FROM THE GEOSPATIAL DISTRIBUTION OF GROUNDWATER ARSENIC IN THE COPIAPÓ RIVER BASIN IN THE ATACAMA REGION OF CHILE

The presence of arsenic (As) in groundwater in the Copiapó River Basin in the Atacama Region of Chile presents a significant environmental challenge, as of the 226 water samples from the wells used for irrigation, mining operations, and domestic use, 86 have As concentration above 5 µg/L, while 16 have As above the WHO (2017) recommended and Chilean norm (NCH, 2006) sanctioned maximum permissible limit for drinking water (10 µg/L). Further, 13 samples have As above 60 µg/L, while As concentration in 10 samples ranged between 122 and 684 µg/L. Two samples from the same location showed very high As concentrations of 7820 and 7205 µg/L, usually reported only in geothermal waters (Alam et al., 2023). Although mining and agricultural activities in the area have contributed to and accelerated groundwater As contamination, the principal source is sulfide mineralization, evident from the geospatial distribution of As concentration and mineralized zones. Moreover, potential control of elevation and/or crustal thickness on As concentration in the Copiapó River water samples (Bieger & Alam, 2021) is also evident in groundwater samples. Of the 13 samples with As concentration above 60 µg/L, 10 were collected at the sites above 3000 m amsl, while 3 were from the mining districts. In a nutshell, the geospatial distribution of As concentration in the river and groundwater samples shows strong geological control(s) and origin. It is concerning that groundwater from the sampled wells are used extensively for irrigation purpose, besides mining activities.

References:

Alam, M.A., Mukherjee, A., Bhattacharya, P. & Bundschuh, J., 2023. An appraisal of the principal concerns and controlling factors for Arsenic contamination in Chile. Scientific Reports, 13, 11168. https://doi.org/10.1038/s41598-023-38437-7

Bieger, K. & Alam, M.A., 2021. Factors controlling varying Arsenic concentration in the Copiapó River, Atacama Region, Chile. Proceedings of the 8th International Congress on Arsenic in the Environment (As2021), 7–10 June 2021, Wageningen, The Netherlands.

NCH, 2006. Norma calidad del agua potable, NCH 409/1. https://ciperchile.cl/pdfs/11-2013/norovirus/NCh409.pdf

WHO, 2017. Guidelines for drinking-water quality, 4th ed., incorporating the 1st addendum. World Health Organization (WHO), Geneva, Switzerland. https://apps.who.int/iris/rest/bitstreams/1080656/retrieve