Geochemical partitioning and possible heavy metal(loid) bioaccumulation within aquaculture shrimp ponds

Limited work has been conducted on trace metal(loid) exchange between sediment, water, feed, and shrimp, particularly in estuarine aquaculture environments. To identify metal(loid) sources and the processes controlling bioaccumulation in shrimp, we analyzed paired aquaculture water, sediment, and shrimp samples collected in Southwest Bangladesh in the late dry season (May), as well as several common artificial feeds. Additionally, we analyzed sediment extract samples from 24-hour laboratory batch experiments as an analogue for aquaculture pond sediment porewater to examine element mobilization from pond sediment. Weak correlations between element concentrations in extracts, pond water, and bulk sediment indicate equilibrium with sediment was not achieved in extract experiments or ponds, and that sediment composition has little influence on pond water or shrimp composition. Aquaculture shrimp metal(loid) concentrations were similar to artificial feed but not pond sediment or pond water, suggesting that shrimp composition is mostly influenced by diet. Although arsenic (As) and selenium (Se) were present at high concentrations in shrimp pond waters and sediment, they were often below detection in shrimp. However, the highly toxic metal thallium (Tl) was detected in shrimp at levels that pose significant human health risks based on calculated target hazard quotient (THQ) values. Thus, further research into potential Tl contamination in Bangladesh aquaculture environments is warranted.