T281 Arsenic, Manganese, Chromium, and Other Geogenic Contaminants, Including Radionuclides in Hydrological Systems—Source, Biogeochemical Cycling, Toxicity, and Removal II

Wednesday, 7 November 2018
1:30 PM - 5:30 PM
Room 133

ARSENIC AND OTHER GEOGENIC CONTAMINANTS IN DRINKING WATER IN THE REGIONS AROUND THE LAKE VICTORIA GOLDFIELDS, TANZANIA

Paper number: T281-9
Program: Technical Sessions
Time: 3:25 PM – 3:40 PM

Authors

Abstract

Tanzania faces a serious constraint with the access to safe drinking water especially for the rural communities in Tanzania. Arsenic contamination of surface water and soil has been recently found to be associated with small and artisanal mining activities in many rural communities in the region around the Lake Victoria Goldfields. Rapidly increasing population, have led to an increase in exploitation of shallow groundwater through excavation of hand dug wells, usually at a depth of 10 m, and water from rivers and small reservoir for drinking purpose in rural communities where groundwater is not easily accessible. The majority of the rural water supplies are based on drilled shallow (< 20 m) and deep wells (30 – 70 m) on which hand pumps are installed. The aim of this study is to investigate the occurrence of arsenic and other geogenic contaminants such as Mn, Fe ,B and Cr in groundwater sources in the region. A total amount of 54 water sources were surveyed during the15 days of the campaign, including five different types of sources surface water (n=15) shallow well (n=12), springs (n=8) and boreholes (n=19).

The concentrations of As and other geogenic contaminants are close to the WHO drinking water guideline, with the exception of some localized hotspots in surface water and shallow groundwater in proximity of gold mining activities. Arsenic concentration levels range between 1 and 300 µg/L, with 53% of all analyzed samples exceeding the WHO guideline (10 µg/L). Manganese shows extreme values in six samples with concentrations of up to 327 µg/L. Iron concentrations typically vary between 2.6 and 328 µg/L, however in four occasions values between 548 and 2075 µg/L were measured. In all water sources, chromium levels range between <0.1 and 1.7 µg/L. By comparing the concentrations of principal geogenic contaminants between filtered and unfiltered samples, this study reveals a strong partition of Fe, Mn and Cr onto the particulate fraction. Similarly, the large discrepancies observed between the field and lab measurements of As suggest that co-precipitation with oxide/hydroxides is responsible for the immobilization of dissolved As. This hypothesis is also supported by the oxidizing conditions of the sampled water (Eh > 400mV) and by the results of the geochemical modeling which show over-saturation with regards to Fe and Al oxide/hydroxides.

Geological Society of America Abstracts with Programs. Vol. 50, No. 6

doi: 10.1130/abs/2018AM-324293

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