Abstract

The use of low levels of oxidants as antifouling agents in coastal and estuarine power station cooling water circuits can give rise to concerns over the likely production of chlorination byproducts (CBPs) including organohalogens, of largely cryptic identity, loading and impact. In order to review the current understanding of the degree of impact involved this paper describes a recent collaborative programme of work on CBPs within the wider context of a number of allied studies on power station cooling water entrainment and discharge effects. Bromoform was the single most important CBP found in coastal power station effluents. Although bromoform was found to accumulate in the liver of the sea bass Dicentrarchus labrax (L.) continuously exposed to a chlorinated effluent stream, no otherwise untoward impact on continuously exposed individuals was discerned. Populations of the common blue mussel Mytilus edulis L., likewise exposed, exhibited two responses: a high degree of genoplasticity and the evolution of stress proteins--although both may have been due to thermal rather than toxic stress. Experiments on plankton that simulated the conditions of entrainment within cooling water systems isolated the influence of oxidant usage, with mortality varying between taxa and life stage. The results suggest a very limited impact of oxidant use and the associated CBPs on receiving waters both in terms of plume toxicity or any more widespread ecotoxicological influence. Instead, it is in combination with applied temperature (DeltaT), pressure and the other stressors involved in entrainment within the power station cooling water circuits themselves that an impact is most marked.