Assessment of lead exposure


 Exposure assessment is one component of the risk assessment process that culminates in the characterization of the health risks posed by a chemical to a population (WHO, 2010b). An investigation of lead exposure from recycling should involve identification or confirmation of the source(s) of exposure, determination of the routes and the media by which exposure is occurring, and assessment of the severity and associated health impacts of exposure. Confirmation of exposure and determination of severity and the need for treatment involves measurement of the blood lead concentration, together with a medical examination for signs and symptoms of lead poisoning. The source(s) of exposure can be identified by taking an exposure history and by carrying out environmental investigations

Blood lead measurements

Lead can be measured in a range of human tissues and fluids, including hair, teeth, bone, blood and urine; however, measuring the concentration of lead in whole blood is the most accepted tool for screening, diagnostic and management purposes (WHO, 2011a). This is because there is a large body of information linking blood lead concentrations with clinical effects and treatment outcomes.

 

Moreover, validated analytical methods and reliable blood quality-control and reference materials are available (Barbosa et al., 2005; CLSI, 2013). Analytical techniques include point-of-care devices and laboratory-based methods, and information about the use of these methods can be found in the WHO publication Brief guide to analytical methods for measuring lead in blood (WHO, 2011a). The choice of method is determined by the available resources and the specific needs of the study in terms of limit of detection, number of samples to be analysed and turnaround time. Point-of-care testing for lead involves the use of a portable analytical device that can be taken and used near the site of exposure or patient care. These devices can analyse very small samples taken from a capillary by finger-prick or from a vein. They have a limited operating range and are most suitable for screening purposes: an elevated blood lead concentration should be confirmed by a laboratory method (WHO, 2011a).

 The advantages of a point-of-care device are that:

1) it does not require skilled laboratory personnel for its operation; 
2) it can be used at locations where transport of blood samples to an appropriate reference laboratory is difficult
3) the result can be provided within a few minutes.


 It is extremely important that steps are taken to avoid lead contamination. If the device is to be used in the field then it should be set up in a clean room with adequate precautions to prevent ingress of dust. Laboratory-based methods for measuring blood lead concentrations have greater accuracy and a lower detection limit, potentially as low as 1-2 µg/dL with some methods. Examples include atomic absorption spectrometric (AAS) methods, such as graphite furnace atomic absorption spectrometry (GFAAS), and inductively coupled plasma mass spectrometry (ICP-MS) (WHO, 2011a). An advantage of GFAAS and ICP-MS is that they can measure very small samples, in the range of 10–50 µL, which is useful when testing young children. The more advanced laboratory-based methods are, however, more expensive to buy and run and require specific laboratory expertise.

For all analytical methods some basic principles should be observed. Blood sampling should be performed by a trained health-care worker (WHO, 2010c). Universal biosafety precautions should be observed to avoid transmission of infection. With both venous and capillary sampling there is a risk of lead contamination from the skin. Sample collection should take place in a clean, lead-free environment and the puncture site should be thoroughly cleansed beforehand (CDC, 2013). Venous blood should be collected into tubes containing anticoagulant, preferably EDTA (CLSI, 2013). All sampling equipment should be of good quality and certified free from trace metal contamination. If blood samples need to be transported they should be kept cool, either with cool-packs in an insulated container, or refrigerated until analysis (CLSI, 2013). For point-of-care analysers, note should be taken of any specific temperature requirements for sample storage. Care should be taken to avoid lead contamination of samples during storage, transportation and analysis. 

When choosing a laboratory, it is important to ensure that it has an adequate quality management system in place. Ideally the laboratory should be accredited by a recognized body and should participate in a proficiency-testing scheme for blood lead analysis. An example of such a scheme is the Lead and Multielement Proficiency Program (LAMP)1 , which is provided by the US Centers for Disease Control and Prevention free-of-charge to laboratories around the world. Participation in LAMP does not provide accreditation but it is a means for monitoring laboratory performance. No safe level of lead exposure has been identified; therefore, to determine the blood lead concentration that indicates excessive exposure the value can be compared to a reference value for the population as a whole. This is usually the geometric mean blood lead concentration found in the highest 2.5% or 5% of the population, i.e. the 97.5th or 95th percentile respectively. In the USA, for example, for children under six years the reference value is currently 5 µg/dL, which is the 97.5th percentile blood lead concentration (CDC, 2012). This same concentration is the 98th percentile value for children under 7 years in France (Haut Conseil de la santé publique, 2014). Germany has adopted reference values of 3.5 µg/dL for children aged 3-14 years, 7 µg/dL for women and 9 µg/dL for men (Wilhelm, 2010).


Taking an exposure history

As part of an investigation into an individual’s exposure to lead, a thorough environmental and occupational history should be taken. This should include questions about the following potential sources of exposure: • individual’s occupation, work practices and those of co-habitants; • participation in, or proximity to, lead recycling activities or manufacturing with recycled lead (e.g. fishing weights); • hobbies that might involve lead exposure; • use of traditional medicines; • diet and the possible consumption of foods cultivated on contaminated land or collected from contaminated water bodies; and • source of drinking-water, e.g. piped water supply, wells, river etc. Examples of approaches to history-taking are provided by the US Agency for Toxic Substances and Disease Registry (ATSDR, 2015) and WHO (WHO, 2010a).

Environmental assessment

Lead battery recycling is associated with significant environmental contamination and therefore investigations of off-site contamination are warranted in the vicinity of these facilities. Potential environmental pathways of exposure include soil and dust, air, water and food, and all of these media can be analysed for lead. In most cases there are guideline or reference values or regulatory standards to compare analytical results against, which will give an indication of the importance of that pathway to exposure.

Soil and dust 

Soil and dust samples can be collected and sent to a laboratory for analysis, or concentrations can be measured in situ using an X-ray fluorescence (XRF) device that reports results almost immediately. A strategy should be devised that ensures collection of a representative set of samples. Account should be taken of possible dispersion of lead-contaminated soil from a recycling site to a wider area by wind or floodwaters. A recent publication by the US Centers for Disease Control and Prevention provides guidance on planning and conducting an environmental survey of lead contamination (Hodge et al., 2015). Guidance on soil sampling is also provided by Demetriades & Birke (2015). Documenting a geographical positioning system (GPS) reading at each sample location greatly assists in mapping areas of high and low contamination. Standards for lead in soil exist in a number of countries, and at least one country, the USA, also has standards for lead in household dust. A global review of standards for lead in residential soil found values ranging from 50 to 400 mg/kg (Jennings, 2013). The standard for non-residential soils may be higher. In the USA, for example, the federal standard for residential soil in areas where children play is 400 mg/kg (US EPA, 2001). The USA standard for lead in household floor dust is 0.043 µg/cm2 (US EPA, 2001).

Air

As described above, various stages in the recycling process can result in the release of lead fumes and particles in the air. Studies have shown that there is high airborne lead exposure in lead-acid battery recycling facilities (Gottesfeld & Pokhrel, 2011; Were et al., 2012). Airborne lead concentrations have been shown to correlate with blood lead concentrations in workers (Were et al., 2012). Airborne lead eventually settles and contaminates surrounding surfaces. In an occupational setting there are two ways of measuring airborne lead levels: area air sampling and personal sampling. Area air sampling involves placing a pump in the work area being tested. The pump runs for a specific period of time (usually corresponding to the normal working day) at a specific flow rate. Air sampling can provide a general overview of the air quality and helps to determine whether further (personal) sampling is needed (US EPA, 1993). A personal air sampling pump is worn by an individual to assess their exposure to lead over a period of time, e.g. a working day (US EPA, 1993). This method monitors air concentrations in a worker’s breathing zone to measure representative employee exposures. The equipment comprises a battery-operated pump and sample medium, which the individual can wear, for example, hung from their belt. A tube is attached to the pump and the other end of the tube is clipped at the collar area close to the person’s breathing zone. Samples are then taken to a laboratory for analysis of total lead. Examples of workplace exposure limits for airborne lead are given below: • Australia: 0.15 mg/m3 as an 8-hour time-weighted average (Safe Work Australia, 2013) • European Union: 0.15 mg/m3 as an 8-hour time-weighted average (EC, 1998) • Mexico: 0.05 mg/m3 as an 8-hour time-weighted average, 40 hours per week (CEC, 2016) • USA: 0.05 mg/m3 as an 8-hour time-weighted average (OSHA, 1978). A number of countries have ambient air quality standards for lead concentrations in the outdoor environment. The guideline value set by WHO for the annual mean concentration is 0.5 µg/m3 (WHO, 2000) but it should be noted that this is not a health-based standard. A detailed discussion of methods for monitoring pollutants, including lead, in ambient air can be found in the WHO publication Monitoring ambient air quality for health impact assessment (EURO, 1999). Examples of national standards are: • Australia: ambient air quality standard: 0.5 µg/m3 averaged over one year (NEPC, 2016) • China: ambient air quality standard: 0.5 µg/m3 averaged over one year, with a seasonal limit of 1 µg/m3 (MoEP, 2012) • EU limit value: 0.5 µg/m3 averaged over one year (EC, 2008) • US National Air Ambient Quality Standard: 0.15 µg/m3 , 3-month average concentration (US EPA, 2016).

Food and water 

Foods that could become contaminated with lead include fruit and vegetables (especially leafy vegetables) grown on land close to recycling activities, foraging animals such as goats, sheep, pigs and poultry, and fish and shellfish caught from waters contaminated with recycling waste.

A common source of water contamination in piped water supplies is the use of lead materials in the water distribution system; however, this is outside the scope of this document. Lead-acid battery recycling can contaminate surface waters that are used for drinking, cooking and bathing. Dissolved lead can percolate through soil into groundwater (UNEP, 2004). If the exposure history suggests that consumption of contaminated food and/ or water is a source of exposure then these can be analysed. The Codex Alimentarius provides a list of maximum permissible levels of lead in selected foods (FAO, 2016). Most countries have a drinking-water standard for lead and the WHO guideline value for drinking-water is 10 µg/L (WHO, 2011b).

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