Geochemical speciation of metals (Cu, Pb, Cd) in fishpond sediments in Batan Bay, Aklan, Philippines

Batan Bay in Aklan, Philippines supports a population largely dependent on coastal fisheries. The development of aquaculture technologies coupled with over-crowded fish pens has negatively affected its natural dynamics and environmental quality. Land-use activities including ports and shipyard further aggravate the problem by contributing to chemical pollution. The present study applied sequential extraction techniques to determine the geochemical speciation of metals in fishpond sediments. Samples were processed and analyzed for Cu, Cd, and Pb using flame atomic absorption spectroscopy. Copper (Cu) showed the highest concentration (10.61–66.81 μg/g-dry weight of sediment). Lead (Pb) content ranged from below detection limit to 15.14 μg/g, while Cd concentration ranged from below detection limit to 2.50 μg/g. Fractionation study showed that the Cu present in the fishpond sediments is mostly non-residual (50.03–73.34%) and significantly associated with the oxidizable fraction (33.89–64.75%). In contrast, the residual fraction served as the dominant host of Pb (33.55–62.68%) in the sediments. Comparison of the results with US EPA and NOAA sediment quality guidelines also revealed that the Batan Bay sediments may be considered generally non-polluted with respect Cu, Pb, and Cd, and not expected to cause adverse effects to aquatic organisms under normal conditions. However, under certain redox conditions, most of the sites may be considered moderately polluted as a result of Cu mobilization from the non-residual fractions of the sediments. Overall, geochemical speciation studies in an important fishery area like Batan Bay will provide valuable insights into the availability of metal contaminants to aquatic organisms under certain environmental conditions.