The effect of sewage on trace metal concentrations and scope for growth in Mytilus edulis aoteanus and Perna canaliculus from Wellington Harbour, New Zealand

Abstract

Trace metal data are reported for Mytilus edulis aoteanus and Perna canaliculus, sampled monthly for 16 months from sites at varying distances away from a major municipal sewage outfall at the entrance to Wellington Harbour, New Zealand. The data indicate that the sewage outfall is the most likely input source of Ag, Cu, Pb, and Zn in this region, and that marine communities up to 3 km east and up to 750 m northwest of the outfall are periodically exposed to the effluent. However, only mussels within 750 m of the discharge point have elevated levels of potentially toxic metals and only M. edulis aoteanusfrom within 100 m of the outfall had higher concentrations of Pb and Zn than are permitted in shellfish for human consumption under N.Z. regulations. Scope for growth of both species, determined during a 3-month period, showed that the effluent adversely affected the physiological condition of these species at sites within 750 m of the discharge. Data for P. canaliculus from an uncontaminated area of Wellington Harbour transplanted into the effluent at increasing distances from the outfall and analysed for trace metals and scope for growth after 1, 2 and 3 months exposure, also indicated that trace metal levels and scope for growth in these mussels were affected by proximity to the outfall.