Effects of heavy metals speciations in sediments on their bioaccumulation in wild fish in rivers in Liuzhou-A typical karst catchment in southwest China.

Although fish are widely confirmed to be susceptible to heavy metals (HMs) contamination in sediments, this bioconversion haven't been detailed. This is especially the case in karst areas, where HMs are less stably retained in the sediments and are more bioavailable. Therefore, we surveyed representative karst rivers in Liuzhou, China, in order to study the relationship between the speciations of seven HMs in the sediments with their bioaccumulation in wild fish. The results showed that the HMs in sediments are all below their permissible exposure limit (PEL), but Cd and Zn are significantly higher than soil basline. Most HMs are in residual fraction, while their exchangeable fractions are present in extremely low proportions. The concentration of Zn, Cr and Cd in some fish are above their maximum recommended limit (MRL). The concentrations of most of the HMs in the fish are significantly correlated with the levels in the sediments and given the higher correlation coefficients for their carbonate-bound phase, this phase can be seen to play a critical role in HMs bioconversion. However, the presence of this phase in low proportions enables other phases, especially oxidizable form, to play a greater role in HMs bioaccumulation. Apart from Do, HMs in the fish samples are significantly correlated with multiple environmental factors, demonstrating environmental fluctuations can manipulate HMs bioconversion from sediments; however, their significance depend heavily on the proportion of particular species. HMs in reducible and oxidizable fraction are more important in regulating, rather than promoting, their bioconversion during environmental fluctuations. Fluctuations in EC, TDS and pH can increase the impacts of HMs in carbonate-bound fraction on their bioconversion. Given the higher background values of EC and TDS and lower pH values during the monsoon period, careful attention should be paid to the increased bioconversion of HMs in karst rivers during this season.