Mersey Estuary (U.K.) Bird Mortalities – Causes, Consequences and Correctives

Abstract

In late 1979 there was an extensive mortality amongst the newly arrived over-wintering populations of waders, wildfowl and gulls in the Mersey Estuary. Mortalities on this scale were unprecedented in the area and there was no obvious cause although circumstantial evidence collected during the months following the incident indicated the probability of acute poisoning by trialkyl lead compounds. The principal source of trialkyl lead compounds was the discharge to the Manchester Ship Canal from a factory producing tetraalkyl lead petroleum additives. Under certain conditions of freshwater flow and tidal movements appreciable concentrations of trialkyl lead could occur in the adjacent waters of the Mersey Estuary. The persistence of trialkyl lead in the estuarine waters provided a suitable source for its up-take by benthic fauna and subsequently birds in amounts similar to those shown to be acutely toxic in laboratory experiments. Simple empirical models were used to calculate an appropriate effluent quality standard to protect waders and wildfowl. Full co-operation was received from the factory concerned and the levels of trialkyl lead discharged have been reduced to the standard. Levels of alkyl lead in the water and in estuarine fauna have fallen in line with the reduced discharge. No bird mortalities attributable to alkyl lead have been observed since the lower discharge levels have been consistently achieved.