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Review of the latest evidence on lead and estimation of intake via drinking water - WT1267

1. Background

Lead is not generally found in raw waters but it can arise in drinking water from the dissolution of lead pipework or lead solder. Neither of these products are permitted for use in contact with drinking water though they may be included in plumbing in older properties.

Lead is a cumulative poison and the WHO guideline value1 (10 µg/L) is based on the principle that there should be no accumulation of the body burden. The effect of lead on IQ is well established but questions are now being raised about whether the existing blood level of concern (10 µg/dL) is appropriate2,3 . Small effects on behaviour and IQ are difficult to measure and it can be difficult to account for possible confounders. In particular such small effects may be vastly outweighed by social and parenting factors4. These considerations may not have direct implications for the WHO guideline value. However JECFA5 has withdrawn its provisional tolerable weekly intake (PTWI) which is the basis of the WHO guideline value.

Lead in drinking water has always been a minor source of exposure compared to other routes of intake. However control measures have been introduced to reduce exposure to lead across the board, for example the changes to unleaded petrol and lead free paint. The introduction of plumbosolvency control has significantly reduced exposure via drinking water. Intake of lead via drinking water is a complex issue. It is affected by the nature of the plumbing at the property, the nature of the water, particularly its hardness, pH and the presence of phosphate and the habits of the consumers, for example, whether they flush the tap prior to use. One of the objectives of the proposed study is to update existing data on lead intake from drinking water by doing a short duration intake study.

The Inspectorate has already commissioned some work to estimate the exposure to lead via drinking water for the population as a whole. This project will build on that by measuring the current intakes of lead via drinking water by consumers at specific properties.

2. Purpose

To critically appraise the recent data on lead intake and adverse effects on health. To review the studies and information on intake of lead via drinking water. To determine current intake of lead from drinking water for consumers living at different property risk groups.

The objectives are to:

1) Critically appraise the recent data on lead intake and adverse effect on health, focusing, but not limited to, studies relating to intellectual and behavioural effects on children;

2) Interpret these studies in the context of previous knowledge of lead toxicity and other factors that influence intellectual and behavioural development;

3) review previous studies that estimate lead intake from drinking water;

4) identify properties that fall into different lead risk groups. For example the highest property risk group would be properties with lead plumbing and without plumbosolvency control. Other group would include properties with lead plumbing with plumbosolvency control, properties with lead solder or high lead fittings (with and without plumbosolvency control) and properties with no evidence of lead in the supply pipes (essentially a control group);

5) conduct a short duration intake study for consumers at the indentified property to measure their lead intake from drinking water over a period of a week;

6) collect and analyse any samples in accordance with best practice including AQC

7) collect or record other relevant water quality data;

8) compare the findings of the study with existing estimates of lead intakes for the population as a whole from drinking water and from other routes of exposure and any historic data identified at objective 3

The review of health data (objective 1) has been triggered by the recent data on intellectual and behavioural development described above. Potential contractors will need to propose how far beyond this the scope of the review needs to be. The Inspectorate understands the next most sensitive effect is on blood pressure but there may be other effects that need to be considered.

The objective 4 specifies five different property risk groups - this is anticipated to be the minimum, potential contractors may propose further groups if they consider it justified. The contractor will need to liaise with water companies and consumer to identify the relevant properties. It is anticipated that a small number of properties will be identified for each group, indeed identification of lead plumbed properties not subject to plumbosolvency control may prove difficult. Potential contractors should propose the number of properties to be included in each group and the robustness of the results. It is open to potential contractors to propose a number of different sample sizes, with different associated cost and to explain how representative each sample size will be. Potential contractors may wish to include more properties in the high property risk groups than in the control, as the control group is unlikely to yield many detectable concentrations. The contractors will need to consider the make-up of the household and should ensure some children are included in each property risk group.

Objective 5 requires a short duration drinking water intake study, the contractor should follow best practice in designing and conducting the study. One study types is a duplicate intake study - in this type of study each time a consumer has a drink, a duplicate sample (an equal volume of the same water) is collected for analysis. There may be a number of different approaches to such a study, for example daily composite samples could be collected for each consumer within the property over a period of one week, giving seven daily intake values. The potential contractors may propose other study types or approaches if they wish.

The study is only intended to examine that aspect of lead intake that comes from tap water. Though unlikely to be significant, the study will need to exclude any intakes from drink additives, drinking vessels or bottled water. A significant volume of water consumed has been boiled and consideration needs to be given to dissolution of metals in kettles and how this can be distinguished from intake from tap water. Equally many of the consumers will drink water away from home and consideration will have to given to how to collect samples or how to estimated the contribution of such drinks to overall lead intake from drinking water.

Objective 6 requires sampling and analysis in accordance with best practice. Potential contractors will need to give thought to using a sufficiently sensitive method of analysis that is able to detect lead in any sample taken, for example, composite daily samples. Normally the Inspectorate requires analysis to the standard for drinking water compliance, for example, at a laboratory meeting the UKAS DTWS and compliance with the AQC procedures specified in NS30. This study is directed at lead but potential contractors may include other analytes where this may enhance the study at minimal additional cost.

Under objective 7 contractors will need to consider any chemical or physical factors likely to influence lead concentrations if those factor have not already been included in the property risk group selection.

Objective 8) requires consideration of exposure via other relevant routes. No measurements are required rather existing data will be collated. The routes that need to be considered include exposure to lead via old paints, soil, traditional remedies, old fashioned cosmetics, lead glazed pottery, leaded crystal, occupational routes etc. Dietary intake is likely to be important. Data are available from the Food Standards Agency, for example, the Total Diet Study6 includes information on metals such as lead.
Project Documents
• FRP - Final Report : DWI70-2-277   (4581k)
• EXE - Executive Summary : DWI70-2-277exsum   (81k)
Time-Scale and Cost
From: 2011

To: 2013

Cost: £105,253
Contractor / Funded Organisations
Institute of Education
Drinking Water              
Fields of Study
Water Quality