TRACE METAL GEOCHEMICAL CYCLING IN SHRIMP PONDS IN SOUTHWEST BANGLADESH: INSIGHT INTO MOBILITY AND POTENTIAL UPTAKE BY SHRIMP

Little research has been performed in regards to surface water chemistry in shrimp ponds in Bangladesh, which can give insight into the migration and mobility of potentially harmful heavy metals such as arsenic (As). Water samples were collected from shrimp ponds in Southwest Bangladesh in 2016 and 2018, and analyzed for metals using an ICP-MS. Data were combined with 2012-2013 data for samples collected in the dry season from Ayers et al. (2017, Geochem. Trans. 18:4). Arsenic levels in 2016 and 2018 samples do not exceed WHO drinking water guidelines (10μg/L), even though 78% of the shrimp ponds from 2012-2013 samples exceed WHO guidelines. Another potential element of concern, manganese (Mn), shows very high levels (>400μg/L) in some shrimp pond samples from 2012-2013, but with much variability. However, in all samples taken in July of 2018 during the wet season, Mn levels were very low (<4μg/L). Wet season July 2018 samples show iron (Fe) levels much higher than dry season 2012-2013 samples, which were collected within a smaller spatial area. July 2018 samples also show strong positive linear trends between As and Fe, and As and copper (Cu), with two distinct subpopulations based on water salinity. This suggests either the sourcing of water and/or salinity has an effect on dissolution of arsenic and copper-bearing hydrous ferric oxides (HFOs), or that chalcopyrite is a source of As, Cu and Fe. Samples of shrimp from the July 2018 surface water sites were also analyzed for trace metals, including As, with results forthcoming.