ACCUMULATION OF CHROMIUM BY A POPULATION OF MUSSELS (MYTILUS-EDULIS (L.)) EXPOSED TO LEATHER TANNERY EFFLUENT

The accumulation of chromium was investigated at the tissue and ultras tructural level in mussels (Mytilus edulis (L.)) in an estuary receivi ng leather tannery effluent and at a reference site. Mussels were also reciprocally transplanted between the estuaries to follow short-term patterns of accumulation and depuration, respectively. The digestive g land was found to accumulate the highest concentrations of chromium in transplanted mussels after 12 months. However, in native mussels (>8 years old), the gill contained the highest concentrations. The general trend in the chromium concentrations of native mussels was: gill > ki dney > digestive gland > mantle > adductor muscle. Concentrations of c hromium in the gill of mussels close to the tannery outfall were in th e range 400 to 1,000 mu g/g dry weight, compared to a maximum of 6 mu g/g in reference mussels. Seasonality in chromium concentrations was s een at both sites with an early spring maximum evident in reference mu ssels that could be linked to spawning and an early summer peak in con centrations in the contaminated estuary, possibly as a result of augme nted feeding or increased discharges. Relationships between tissue con centrations were also studied and a high correlation occurred between some tissues, for example, digestive gland-kidney and gill-adductor mu scle. Depuration was generally slow in mussels transplanted out of the Colligan Estuary, although the digestive gland lost the most chromium . Therefore, it is suggested that two pools of chromium accumulation e xist in the contaminated mussels, that is, via the gills (slow) and vi a the digestive gland (fast). At the cellular level, chromium was foun d in both particulate (lysosomal) and cytosolic fractions. In the gill , particulate chromium was associated with calcium and phosphorus, whe reas chromium was detected in sulfur-dominated granules in the kidney. In the cytosol, binding to a high molecular weight component occurred in the gill, whereas binding in the digestive gland cytosol was domin ated by a poorly resolved low molecular weight component. In addition, chromium is apparently detoxified by a separate pathway compared with iron or zinc, as judged by the differential cytosolic and lysosomal a ffinities of these metals.