Influence of sediment acidification on the bioaccumulation of metals in Ruditapes philippinarum.

BACKGROUND, AIM AND SCOPE: The influence of pH (range 6.5-8.5) on the uptake of Zn, Cd, Pb, Cu, Ni, Cr, Hg, and As by juveniles of the clam Ruditapes philippinarum was examined in order to understand whether variation in sediment pH has significant repercussions on metal bioaccumulation.

MATERIALS AND METHODS

Clams were exposed to sediments collected in three locations in the Gulf of Cadiz (Huelva, Guadalquivir and Bay of Cadiz) and to contaminated particles derived from an accidental mining spill in Spain.

RESULTS

With a notable exception of metal Cd, the concentration of metals within clams significantly increased (p < 0.1) when sediment pH was lowered by one or two units. Moreover, the magnitude of this effect was dependent on the type of sediment contamination.

DISCUSSION

Lower pH increases metal solubility and reduces or invert the metal sorption of metals to sediments. Increases in free metal ions in water favors metal uptake by clams, hence pH is an important factor controlling the mobility of these metals within sediments and their subsequent bioaccumulation within biota. Although sediment-water exchange of Cd can increase with acidification, this excess may be counterbalanced by the presence of ligands in seawater preventing the uptake by organism. Besides chlorines, Cd has also an affinity with carbonates and other ligands present in sea water. These Cd-carbonate complexes may reduce the bioavailable to organisms.

CONCLUSIONS

These results highlight the potential implications of sediment acidification, either due to the storage excess of organic matter or to the forced capture of CO(2), on the increasing metal availability to benthic organisms.

RECOMMENDATIONS AND PERSPECTIVES

This kind of studies should be increased to address the influence of acidification in the behavior, bioavailability, toxicity, and risk assessment of contaminants associated with sediments either above sub-seabed geological formations in marine environments or in high enriched by organic matter in estuarine areas. Recently, the capture of CO(2) in marine environments has been approved and started; it is necessary to address the potential impacts associated with leakages or other events occurring during the procedure of injection and storage of CO2.