The main pathways of exposure to lead from recycling used lead-acid batteries arise from environmental emissions. These occur at various stages in the recycling process, as described below. Lead particles and fumes emitted into the air can be inhaled and are also deposited onto soil, water bodies and other surfaces, including in gardens and homes. Waste materials from lead processing can, if not treated and correctly disposed of, contaminate land and water bodies. Used acid with high concentrations of lead is often dumped on land or released into waterways. Lead can enter the food chain through crops growing on contaminated land, from direct deposition onto crops, through food animals foraging in contaminated areas and consuming lead particles, and from fish and shellfish living in lead-contaminated water (UNEP, 2003; UNEP, 2010).
Components of a lead-acid battery
A lead-acid battery is made up of the following components, enclosed within a plastic or ebonite box or casing (see Figure 1) (UNEP, 2003). There are positive and negative terminals made of lead, which provide the connection points to external devices. There are sets of positive and negative plates kept apart by plate separators - porous sheets of PVC or polyethylene plastic, glass microfibre, or phenolic resins that allow the free movement of the ions in the electrolyte solution. The positive plates are grids made of lead or lead alloy coated with porous metallic lead paste, and the negative plates are lead grids coated with lead dioxide paste. A series of negative and positive plates plus separators makes up a battery element, and the battery elements are separated by plates of the same material as the battery box. The elements are bathed in a sulfuric acid electrolyte solution, which can be topped up via the plugs. In sealed batteries the electrolyte is either a gel or is soaked onto glass microfibre separators.
The average amount of lead in automotive batteries can range from 2 to 13 kg, depending on the size of the vehicle (CEC, 2016).
Steps in the recycling process
Almost all parts of a lead-acid battery can be recycled. The main steps in the recycling process are as follows:Collection and transportation of the batteries to a recycling facility
Separation of the component parts of the batteries
Smelting and refining of the lead components
Washing then shredding or melting of the plastic components
Purification and treatment of the sulfuric acid electrolyte
Treatment and disposal of waste
The batteries are mechanically or manually broken up to separate out the acid and component parts. The lead components are conveyed to the furnace for smelting. After smelting the slag is removed and the molten unrefined lead may be poured into moulds and cooled or it may immediately be directed to a holding kettle (cast-iron pot) to keep it molten prior to refining. The aim of the refining process is to produce lead of high purity or to produce alloys (requiring the addition of specific trace elements to the refining kettle) that can be used to make a new lead battery. The molten lead is then cast into moulds and allowed to cool (OSHA, 2002).
Recyclable plastic components are washed then shredded or ground and melted. The molten plastic is extruded into pellets, which can then be used in the manufacture of other plastic goods, including new battery casings (ILA, 2015). In many smaller recycling facilities in low- and middle-income countries, the plastic battery cases are often not recycled and may be dumped or burned.
The electrolyte may be recovered for re-use or neutralized with alkali and treated to remove lead and other contaminants before being released into the sewage system. Alternatively the solution may be purified and sodium sulfate extracted for use in making detergents and other products (UNEP, 2003; ILA, 2015).
At each of these stages, lead fumes and dust are released into the air (see section 2.3), contaminating both the workplace and the wider environment. The use of automated, enclosed processes with pollution control devices can reduce these emissions.
In a typical automated enclosed process, the lead batteries are broken up in a hammermill or shredder and the pieces are fed into tanks filled with water. Here gravity is used to separate the components: the lead and heavy materials sink to the bottom and the plastics rise to the top. The plastic materials are skimmed away and the liquid, including the sulfuric acid electrolyte is drawn off. The metallic components are channelled to closed furnaces for smelting and refining and then piped into casting moulds (OSHA, 2002; UNEP, 2003). Waste from recycling is collected, treated and disposed of at a designated waste disposal site (UNEP, 2003).
In a manual process the batteries are drained then broken up with electric saws, machetes or axes. The components are separated by hand into piles. The lead components are carried to the furnace or taken on an open conveyer belt. The furnace may, in the worst case, be no more than an open pot on a fire (UNEP, 2003; UNEP, 2004; Manhart & Schleicher, 2015). The molten lead is then poured into casting moulds.
Lead release and exposure during recycling
At the collection and transportation stage, the sulfuric acid electrolyte solution is sometimes drained out to reduce the weight of the batteries or because a higher price is offered for drained batteries (Manhart & Schleicher, 2015). If not done at this stage then the electrolyte may be drained out at the recycling site (in some enclosed processes the batteries are not drained prior to crushing). In addition, electrolyte may leak out of damaged batteries during storage and transportation (UNEP, 2003). If adequate precautions are not taken to avoid skin contact, the acid will cause corrosive injury. The electrolyte contains dissolved lead and, if the electrolyte leaks out or is poured onto the ground rather than into collection tanks, the lead becomes incorporated into soil particles, which subsequently become a source of lead dust (UNEP, 2003). Pouring the electrolyte into ponds or streams will contaminate water that may be used for drinking, fishing and cooking.
Manually breaking up the batteries releases lead particles and lead oxide dust, which are a source of lead exposure to the worker (Suplido & Ong, 2000; UNEP, 2003). The dust and particles also settle in the surrounding soil and may be blown to more distant areas, contaminating the wider environment and becoming a source of exposure to the community (UNEP, 2003; Haefliger et al., 2009). Hammermills and shredders may release lead mist, which can dry and release lead dust if disturbed. Dust settled on vibrating equipment can become re-suspended in air and inhaled (OSHA, 2002).
During the separation process, water used in automated systems for separating lead from other components becomes heavily contaminated with lead compounds. If this leaks or is not treated before disposal it will contaminate the ground or soil. As this water evaporates it leaves a residue of fine lead dust that may then be dispersed by wind (UNEP, 2003).
When lead components are moved around the recycling site, e.g. on open conveyor belts or in wheelbarrows, and when they are shovelled into the furnace, lead fragments and dust are released.
The temperatures used for refining lead can be up to 1000 °C, which generates large amounts of lead fume. If the furnace is not under negative pressure or if the plant has inadequate ventilation and/or emission controls, the fumes will be inhaled by workers (UNEP, 2003). Lead fumes are particularly hazardous as the small particle size enables the lead to be inhaled into the lower respiratory tract and absorbed (ATSDR, 2007). The fumes will eventually settle as lead particles on surrounding surfaces and the soil, creating lead dust, which can also be inhaled. Fugitive lead emissions from these sources can be substantial and are more difficult to control. Sometimes ash from the smelting process is manually sifted to retrieve metal particles, dispersing lead-contaminated dust into the air (Paddock, 2016)
Fume, lead particles and dust released at various stages in the recycling process will also settle on the skin, hair and clothes of workers. If workers do not wash and change clothes before returning home this lead becomes a source of take-home exposure to household members and even, potentially, to the wider community (Daniell et al., 2015). Lead poisoning in the spouses and children of lead workers, caused by transfer of lead from the workplace to home, has repeatedly been documented (Baker et al., 1977; Chisolm, 1978).
Informal lead recycling
Non-regulated, informal (“backyard” or “cottage”) recycling practices occur in many countries and have resulted in lead exposure and poisoning, with young children being particularly at risk (Matte, 1991; Suplido & Ong, 2000; Haefliger et al., 2009; van der Kuijp et al., 2013; Daniell et al., 2015). This practice is sometimes carried out in urban areas with high population densities, meaning that a recycling operation has the potential to affect a large number of people (Haefliger et al., 2009). There are few (if any) pollution controls. Lead-containing waste products, such as electrolyte solution and slag from the smelting process are often simply dumped, although slag may also be sold on for further smelting. The work may be carried out by small family groups around the home. Children often assist with dismantling the batteries and washing components (van der Kuijp et al., 2013). Because the recycling process is done with little knowledge of the toxicity of lead, and is conducted under poor conditions of safety, health and environmental controls, informal recycling is particularly likely to result in environmental contamination and human exposure (UNEP, 2004; van der Kuijp et al., 2013; Daniell et al., 2015).Soil contaminated with lead compounds can spread throughout the community and be tracked into homes. If recycling activities take place around the home, then airborne lead can enter the home and accumulate on the floor, on beds and on other furniture (Haefliger et al., 2009). Settled dust can be re-suspended in the air and inhaled as people walk through or brush up the dust. Young children, who spend large amounts of time on the ground and who frequently put their hands and other objects in their mouths, are at particularly high risk of lead exposure in these settings
If the plastic components are inadequately washed before re-use for other products, then these products will be contaminated with lead (Manhart & Schleicher 2015). Battery casings may be used around the home as a construction material or as containers, again introducing the possibility of lead contamination (Daniell et al., 2015).
There have been reports in Cameroon and other countries of lead scrap from informal recycling being mixed with scrap aluminium to make cooking pots (CREPD, 2015). Lead can leach out into food being prepared or stored in these pots (Weidenhamer et al., 2014; Weidenhamer et al., 2017).
Other chemicals released during recycling
While the focus of this document is on the release of lead, there are a number of other hazardous chemicals that can be released during recycling. In addition to the lead terminals and plates, batteries contain various plastics or hard rubber (ebonite) and the sulfuric acid electrolyte solution. The lead components may contain other elements such as arsenic, antimony, barium and cadmium (UNEP, 2003). These substances may form part of the waste and emissions generated at various stages of the recycling
process. The rubber and plastic components may be burned rather than recycled, producing toxic gases, including sulphur dioxide, chlorine, dioxins and dibenzofurans (UNEP, 2003).
Studies of lead exposure from recycling lead-acid batteries
Recycling lead-acid batteries can result in significant occupational exposure to lead. Were et al. (2012) investigated a lead-acid battery recycling plant in Kenya and found elevated concentrations of lead in the air and elevated blood lead concentrations in workers. The study identified a number of weaknesses in work practices and control measures that resulted in excessive exposure to lead. Examples included inadequate engineering controls (including poor ventilation systems) and inadequate personal hygiene measures (including lack of respiratory protection and failure to use washing facilities). Among workers involved in recycling lead-acid batteries there is often poor general awareness of the hazards of lead (CREPD, 2015).A review of published literature on exposures from formal-sector lead-acid battery manufacturing and recycling plants in developing countries found that seriously elevated blood and airborne lead concentrations were common (Gottesfeld & Pokhrel, 2011). In workers involved in battery recycling the arithmetic mean blood lead concentration was 64 µg/dL, with a range of 37.7 to 112.5 µg/dL. This contrasted with data from developed countries where few workers had blood lead concentrations above 50 µg/dL and most were below 25 µg/dL (though even these concentrations are likely to result in adverse health effects – see section 3.2). The review also found that high airborne lead concentrations were reported in recycling facilities, with a mean value of 367 µg/m3. This is 7 times higher than the permissible exposure limit of 50 µg/m3 as an 8-hour time-weighted average (TWA) adopted in the USA (OSHA, 1978).
Communities living near recycling facilities are at risk of exposure to lead, and extensive contamination of soil surrounding many formal sector recycling plants has been reported (Levallois et al., 1991; Wang et al,. 1992; Zhang et al., 2016). In their review, Gottesfeld & Pokhrel (2011) summarized 11 studies in seven countries on lead exposure of children residing near lead battery manufacturing and recycling facilities and reported an average blood lead concentration of 29 µg/dL, with values up to 71 µg/dL. Recently a large recycling plant in the USA was closed down after it failed to meet emission controls and waste management standards. This plant was found to have contaminated the surrounding area with lead to a distance of 1.7 miles (California Environmental Protection Agency, 2015).
The case studies given below illustrate how environmental contamination caused by the recycling of used lead-acid batteries can result in severe lead poisoning in a community, which may continue even after recycling operations have stopped. The first case describes exposure to lead via reclamation of lead and lead compounds from discarded batteries, and the health consequences. The other two case studies show that closing down or moving battery recycling operations are not sufficient measures on their own to prevent human lead exposure.
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