Public health implications of new guidelines for lead in drinking water: acase study in an area with historically high water lead levels

Concern about the neurotoxicity of lead, particularly in infants and young children, has led to a revision of blood lead levels which are considered t o involve an acceptable level of human exposure. Drinking water guidelines have also been reviewed in order to reduce this source of population exposu re to lead. In the last 20 years, guidelines have been reduced from 100 to 50 to 10 mu g/litre. Lead in tap water used to be a major public health pro blem in Glasgow because of the high prevalence of houses with lead service pipes, the low pH of the public water supply and the resulting high levels of lead in water used for public consumption. Following two separate progra mmes of water treatment, involving the addition of lime and, a decade later , lime supplemented with orthophosphate, it is considered that maximal meas ures have been taken to reduce lead exposure by chemical treatment of the w ater supply. Any residual problem of public exposure would require large sc ale replacement of lead service pipes. In anticipation of the more stringen t limits for lead in drinking water, we set out to measure current lead exp osure From tap water in the population of Glasgow served by the Loch Katrin e water supply. to compare the current situation with 12 years previously a nd to assess the public health implications of different limits. The study was based on mothers of young children since maternal blood lead concentrat ions and the domestic water that mothers use to prepare bottle feeds are th e principal sources of foetal and infant lead exposure. An estimated 17% of mothers lived in households with tap water lead concentrations of 10 mu g/ litre (the WHO guideline) or above in 1993 compared with 49% in 1981. Mean maternal blood lead concentrations fell by 69% in 12 years. For a given wat er lead concentration, maternal blood lead concentrations were 67% lower. T he mean maternal blood lead concentration was 3.7 mu g/litre in the populat ion at large, compared with 3.3 mu g/litre in households with negligible or absent tap water lead. Nevertheless, between 63% and 76% of cases of mothe rs with blood lead concentrations of 10 mu g/dl or above were attributable to tap water lead. The study found that maternal blood lead concentrations were well within limits currently considered safe for human health. About 1 5% of infants may be exposed via bottle feeds to tap water lead concentrati ons that exceed the WHO guideline of 10 mu g/litre. In the context of the h ealth and social problems which affect the well-being and development of in fants and children in Glasgow, however, current levels of lend exposure are considered to present a relatively minor health problem. (C) 2000 Elsevier Science Ltd. All rights reserved.