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This paper evaluates the possible biological significance of routine monitoring data for dissolved copper and zinc collected from nine lightly industrialized Essex and Suffolk estuaries by the Environment Agency during the years 1992–96, and investigates the relative importance of the various sources. The annual average concentration data from several locations in each estuary are compared with the proposed revised UK annual average Environmental Quality Standards (EQSs) for dissolved copper (5 μ g l−1) and zinc (10 μ g l−1) in seawater. In summary, 21.7% of sampling-location/year combinations exceeded the revised EQS for copper, and 53.6% exceeded the revised EQS for zinc, and one or more locations on each estuary failed each EQS for at least one year in the five-year period. In some of the nine estuaries, riverine and treated sewage discharges contribute a significant proportion of the total copper and zinc input, but the single largest source of both metals is almost certainly boating traffic employing copper-based antifouling paints and zinc-based sacrificial anodes. The data suggest that both metals may be causing ecological damage, but this cannot be firmly concluded because an unknown proportion of each was probably complexed with dissolved organic matter, and therefore less bioavailable. This question can only be addressed by field studies of the biological status of indicator species in these waters. |
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