Arsenic Concentration in the Surface Water of a Former Mining Area: The La Junta Creek, Baja California Sur, Mexico.

Jobst Wurl,Miguel Imaz Lamadrid,Baudilio Acosta Vargas,Lía Mendez-Rodriguez

doi:10.3390/ijerph15030437

Abstract

The mining activity in the San Antonio-El Triunfo district, located in a mountainous region at 60 km southeast of La Paz, occured for more than 250 years and left behind severe contamination of soils and riverbed sediments which led to elevated concentrations of arsenic and other trace elements in the surface- and groundwater of the region. Although the main mining activity ended around 1911, contamination is still beeing distributed, especially from left behind tailings and mine waste piles. The contamination levels in the groundwater have been reported in several studies, but there is little information available on the surface water quality, and especially the temporal variation. In this study, we analyzed the surface water of the La Junta creek, in the southern part of the San Antonio-El Triunfo mining district. The working hypothesis was that by means of a spatial analysis of surface water and shallow groundwater, in combination with the temporal observation of the concentrations in runoff water, the effects of different sources of arsenic (natural geogene anomalies, due to historic mining activity, and hydrothermal related impact) in the La Junta creek can be recognized. This present study revealed that historic mining activity caused a mojor impact of arsenic but less contamination was observed than in the northern part of the district and elevated arsenic concentrations in stream water generally occurred during times of low streamflow.

Highlights

The level of arsenic in drinking water of rural areas in Baja California Sur is elevated; 16% of the drinking water, obtained from 440 groundwater and surface water samples in the rural areas of the state, was contaminated with arsenic and 4% contained more than 0.1 mg/L arsenic [1].The highest values were obtained from two wells, located in the San Antonio-El Triunfo mining district.This mining district is divided into three watersheds: The northwestern El Triunfo area is situated in the El Carizal catchment and drains to the Pacific Ocean, the northeastern San Antonio area is situated in the Los Planes watershed and drains to the Gulf of California [2]
In congruence with results for the rest of the mining district and nearby areas, the population is exposed to elevated concentrations of arsenic in the surface- and groundwater
One third of the inhabitants surpassed the biological exposition index (BEI) of 35 μg/L. This index defines the permissible limit for occupational exposure to arsenic. The aim of this detailed environmental study was to investigate contamination sources and dispersal resulting from historical mining practices and to distinguish between natural and mining sources of metals/metalloids with a specific focus on the surface water

Summary

Introduction

The highest values were obtained from two wells, located in the San Antonio-El Triunfo mining district. This mining district is divided into three watersheds: The northwestern El Triunfo area is situated in the El Carizal catchment and drains to the Pacific Ocean, the northeastern San Antonio area is situated in the Los Planes watershed and drains to the Gulf of California [2]. The southern area of the mining district represents the smallest part and belongs to the Cañada Honda watershed, which drains to the Pacific Ocean (Figure 1). Public Health 2018, 15, 437; doi:10.3390/ijerph15030437 www.mdpi.com/journal/ijerph

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