LONG-TERM STUDY OF MERCURY CONCENTRATIONS IN FISH FOLLOWING CESSATIONOF A MERCURY-CONTAINING DISCHARGE

Mercury-contaminated industrial effluent was discharged over a 30-year period Bite Princess Royal Harbour, a marine embayment on the south c oast of Western Australia. The discharge of effluent was stopped in 19 84 and most fish taken from the harbour at that time contained concent rations of Hg in their muscle tissue which exceeded the maximum permit ted concentration (0.5 mg kg(-1)) set by Australian health authorities . To allay human health concerns, the contaminated portion of the harb our was closed to all forms of commercial and recreational fishing in 1984. The course of Hg contamination following cessation of the efflue nt discharge was monitored by determining Hg concentrations in the mus cle tissue of eight teleost fish species, namely cobbler (Cnidoglanis macrocephalus), rock flathead (Platycephalus laevigatus), striped trum peter (Pelates sexlineatus), King George whiting (Sillaginodes punctat a), Australian herring (Arripis georgianus), brown-spotted wrasse (Pse udolabrus parilus), spiny-tailed leatherjacket (Bigener brownii) and s ix-spined leatherjacket (Meuschenia freycineti), sampled near the effl uent outfall on 14 occasions from 1984 to 1993. Mercury, concentration showed a significant positive relationship with length of fish for fi ve of the species and a significant negative relationship with length for two species. Four species showed significant differences in Hg con centration depending on season (summer vs winter); summer concentratio ns were generally higher than those in winter. The Hg concentrations d ecreased with time and were about 50% elf their initial values by 1993 . In general, fish Hg levels had decreased to below the maximum permit ted concentration by 1991 and the closed portion of the harbour was re opened in 1992. For most species, however, the rate of reduction in Hg concentration was less in the latter part of the study. The data sugg est that future reductions in Hg concentrations in fish may be less th an those achieved in the first 10 years, and that for some species Hg concentrations could remain elevated for many years. Copyright (C) 199 6 Elsevier Science Ltd