Lead in drinking water: public health, mitigation and economic perspectives
In Scotland, public water supplies are lead-free. However, water from corrosive (acidic, soft) raw sources may be a problem for premises still containing lead pipes and plumbing components such as lead-solder and brass fittings due to plumbosolvency, i.e. lead leaching from leadcontaining pipes and plumbing. Exposure to lead in tap water is entirely preventable, but a better understanding of the effectiveness of lead corrosion control is required. This report reviews national and international evidence on the public health and economic aspects of lead in drinking water, from research carried out over the last 50 years, to contribute to this understanding. The evidence reviewed showed a fast evolution in the scientific understanding of the adverse and irreversible, in many cases, health effects of lead exposure. The consensus among scientists is that the focus of regulation and preventative policies should be to keep exposure in the range of blood lead levels of 2-10 μg/dl because exposure to greater levels is now rare.
Legislation has caught up with this knowledge leading to strict controls on lead uses and emissions and lead-free petrol, paint and food cans. However, lead is still in use in certain sectors of
industry because of its unique and irreplaceable properties (e.g. acid lead batteries). Background lead levels in the environment have declined by more than 90% since the 1990s but they are not at zero levels. Large amounts of lead have been stored in the environment (e.g. soil) because of historical every day and industrial uses of lead, thereby potentially contaminating food and outdoor and indoor dust. Old housing may still contain leaded paint and some toys still contain lead. The water distribution systems in many countries still contain lead supply pipes and lead in premise plumbing components in ever decreasing percentages. Chemical lead corrosion control is the most commonly used strategy to mitigate lead in tap water and protect public health from the adverse effects of low lead exposure.
The review of the national and international literature on lead in drinking water showed that there is sufficient and robust scientific evidence on
(i) the contribution of water lead on individual lead exposure;
(ii) the adverse health effects and social outcomes of lead exposure in childhood;
(iii) the shortcomings and cost of lead mitigation practices; and
(iv) the public health and monetary benefits of lead-free practices.
The predominant source of lead in drinking water is lead-containing piping and plumbing. No safe level or threshold for lead exposure has been agreed by experts. The World Health Organisation has identified lead as a chemical of major public health concern. Low exposure to lead (i.e. blood lead concentrations below 10 μg/dl) in children has been associated with
intellectual impairment in childhood, and cognitive deficit, loss of individual potential and low income in adulthood.
The World Health Organisation has warned that there may be a risk for bottle-fed infants through intake of drinking water with a lead concentration of 10 μg/L.
In Scotland, water mains and communication pipes to properties’ water meter are lead-free: Failures of the water lead standard (i.e. 10 μg/L) concern a small percentage of properties still
containing lead pipes on homeowners’ side of the water meter and within premises. Optimised orthophosphate dosing (i.e. the dose required to achieve compliance with the water lead standard of 10 μg/L) has been shown to effectively reduce lead leaching from lead pipes and brass fittings within premises. However, it is not a lead-free strategy. Total lead pipe replacement (i.e. replacement of lead pipes in utility’s and homeowners’ side) can be a leadfree strategy. However, homeowners’ cooperation has generally been poor, irrespective of the availability of state-funded lead pipe replacement grants, because of the disruption and inconvenience involved and the cost incurred in case of means-tested grants.
Since the 1970s, lead-free policies (e.g. gradually phasing lead out of petrol) and the tightening of the standard for lead in drinking water (i.e. from 100 μg/L to 10 μg/L) co-occurred. This makes it difficult to separate the benefits of water lead mitigation to the proportion of the population consuming lead contaminated water from the benefits of phasing lead out of petrol to the general population and the environment. The greatest economic benefits to the society of removing all sources of residential lead (including lead pipes and plumbing) arise by avoiding the health and social costs of low lead exposure in the affected oportion of the population. These costs refer to provision of medical treatment and special education; combating lead-linked crime; and loss of life-time earnings and contribution to general productivity due to poorer individual potential.
This report has provides sufficient evidence and context to analyse and evaluate the public health and economic implications of lead-free drinking water in Scotland.