E-waste is a term used to describe discarded electronic goods such as computers, televisions, cell phones, photocopiers, facsimile machines, audio and stereo equipment. In 2006, the world production of e-waste was estimated at 20 - 50 million tonnes per year by the United Nations Environment Programme, with a major component of it being produced in Europe, the United States and Australasia. It is estimated that China, Eastern Europe and Latin America will become major e-waste producers in the near future. In recent times, e-waste production has been driven by the rapid growth in computing. Although PBDEs are either banned or severely restricted, since their use was widespread prior to this, they are now entering the waste stream, as goods treated with them in the past are now reaching the end of their useful life. In the next five years, one billion computers are expected to become e-waste!
E-waste is both physically and chemically different from other forms of waste as it contains hazardous substances as well as those of value. Although its exact chemical composition depends on the type of discarded item, age and country of origin, the valuable components of e-waste in most products include copper, aluminium, iron and platinum group metals.
All e-waste contains flame retardants as this is a mandatory requirement in electronic goods, their use being mainly in the plastic outer casing. They are also extensively used in printed circuit boards. Flame retardants are substances that are incorporated into flammable material to slow down and/or inhibit a developing fire. Therefore, they perform an important function by reducing the number of fires and limiting the consequences of fires that develop. Polybrominated diphenyl ethers (PBDEs) were one of the flame retardants of choice and were added at concentrations between 5 – 30% by weight. Metals such as lead, mercury, cadmium and nickel are also found in these goods as they are used in LCD displays, fluorescent lamps, batteries, switches, toners etc. PBDEs and these metals are toxic. Therefore, special care is required when handling, storing and recycling e-waste in order to avoid environmental contamination and detrimental effects to human health.
Polybrominated diphenyl ethers (PBDEs)
The concept of using flame retardants is not novel. It dates back to about 450 BC when the Egyptians used alum to reduce the flammability of wood. The Romans used a mixture of alum and vinegar to reduce the combustibility of wood. During the 17th century, inorganic compounds such as ammonium salts were used to protect the textiles and property of King Ludwig XIV of France. With the advent of a variety of new polymeric material in the 20th and 21st centuries, many of which were flammable, more extensive use of flame retardants became a necessity.
The choice of a flame retardant depends on a number of factors such as, the material to be flame retarded, the fire safety standards with which the product must comply, stability during life time of product, compatibility with the polymer, cost and recyclability. Of the flame retardants, currently in use, the most widely used are the brominated flame retardants (BFRs) as they are the most effective when both performance and cost are considered.
BFRs are categorized as ‘reactive’ and ‘additive’ flame retardants based on their mode of incorporation into the polymer matrix. Reactive flame retardants are chemically bonded to the polymer matrix and hence remain intact during and after the life time of the product. Additive flame retardants on the other hand are simply mixed in with the polymer matrix and hence are able to leach out of the product. PBDEs are additive flame retardants.
Commercial production of PBDEs
PBDEs were typically manufactured commercially as three mixtures, namely, pentaBDE, octaBDE and decaBDE. Due to concerns about their adverse impact on the environment and on humans, in 2004, the EU and North America ceased production of penta and octaBDE commercial mixtures, and their use in all applications. They were categorized as persistent organic pollutants (POPs) in 2009, and were included in the Stockholm Convention for elimination.
|This figure shows the fluxes of contaminants associated with e-waste from producers to receivers and ultimately to humans (Re-drawn from Robinson, 2009, Sci. Total Environ.)|
In 2008, decaBDE was restricted in the EU, and US manufacturers voluntarily committed to phase out its use in the US by December 31, 2013. However, decaBDE is still in use in many countries primarily in high impact polystyrene casing for electrical and electronic goods. There is much lobbying for decaBDE to be also included in the Convention.
It is noteworthy that despite the restrictions and bans on their manufacture and use, these chemicals are still released both from products remaining in use and from obsolete electrical and electronic goods (e-waste) at waste treatment facilities.
Mode of action
PBDEs act by interfering with the radical mechanism that takes place in the gas phase during combustion. The combustion process can be subdivided as; preheating, volatilization/ decomposition, combustion and propagation.
In the pre-heating step pyrolysis of the material occurs to give solid, liquid and gaseous products. The gaseous products ignite thereafter generating flames and high energy free radicals such as H, OH, and OOH radicals. These radicals are responsible for the propagation of the flame.
PBDEs decompose at a lower temperature to that of the polymer matrix to give bromine radicals. The bromine radicals so generated ‘capture’ the high energy H, OH and OOH radicals, thus hindering the spread of the fire.
PBDEs are a popular choice as flame retardants as they are resistant to acids, bases, oxidizing and reducing agents, heat and light. However, these same properties prove to be a disadvantage when PBDEs are released into the environment. As they are persistent and have a high affinity for lipids (as seen by their high log KOW value), they readily bioaccumulate in organisms and biomagnify in food chains. Since PBDEs have the ability to undergo long range atmospheric transport (known as the Grasshopper effect), they are able to travel to destinations far from their origin. PBDEs are also released into the environment during transport of e-waste to disposal sites and their subsequent storage, prior to sorting out, deposition or recycling.
One of the most important end points of PBDE toxicity in human / animals is disruption of thyroid homeostasis. The toxic effects are caused by hormone mimicry as metabolites of PBDEs closely resemble the thyroid hormones T3 and T4. Hence, PBDE metabolites also bind with a high affinity to the thyroid receptors resulting in a lowering of blood levels of thyroid hormone.
PBDEs also adversely affect neuro behavioural development, cause hepatotoxicity at relatively high doses, are associated with reduced fertility, and early onset of puberty. They are a possible cause of cancer.
Fate of E-waste
E-waste is disposed of with the ‘normal’ municipal or industrial waste which generally ends up in landfills, or it is recycled.
Landfill has been a dominant option for waste in developed countries for many years, where both hazardous and non-hazardous wastes were disposed of together in the same landfill (co-disposal). With a view to reducing the environment impact of landfills and risk to human health, co-disposal is no longer practiced in many Western countries. Landfills are now categorized as, landfills for hazardous waste, landfills for non-hazardous waste, and landfills for inert waste, and only specific waste types may be disposed of in them. Further, some nations have imposed the requirement that waste should be pre-treated before being sent to landfills. This directive aimed at increasing waste recycling and recovery and reducing emissions from landfills. The directive also places more stringent engineering and operation conditions on landfill operators, to ensure that groundwater quality is not compromised. As such, monitoring both leachate and groundwater for a range of specified hazardous substances is mandatory.
It is now also mandatory for new landfills in developed nations to be engineered using a liner membrane barrier to separate the landfilled waste from the underlying ground. However, since all membranes are slightly porous, low volumes of leachate cross the membrane. Therefore, modern landfill designs delay, but do not wholly prevent ground and surface water pollution.
Further, a series of leachate collection pipes is laid on top of the membrane to transport the leachate to a collection or treatment location. These leachate collection systems are prone to failure as the landfills age and hence pose a significant risk to groundwater.
Since virtually all e-waste contains valuable materials, copper in particular, this provides an incentive for recycling. Reusable components and base materials (i.e. copper and precious metals) can be recovered during recycling. However, rich countries generally do not recycle e-waste due to high labour costs, lack of facilities and tough environmental regulations. Instead, it is disposed of in landfills or exported to poor countries for recycling, where recycling takes place using primitive methods and little regard for worker safety. E-waste exportation is illegal under the UN Basel Convention. However, it takes place through clandestine operations, legal loopholes (e.g. exporting broken equipment under the pretence that it is functional and therefore not waste) and by countries that have not ratified the Convention.
Of the collected e-waste, it is estimated that 80% is exported to poor countries for recycling. China receives 70% of the exported e-waste. Significant quantities are also exported to India, Pakistan, Vietnam, the Philippines, Malaysia, Nigeria and Ghana. Due to the clandestine nature of these operations, the actual mass of e-waste being exported cannot be quantified.
‘Reuse’ is yet another source of e-waste for poor countries, where electronic equipment which is obsolete in rich nations is shipped by “well-meaning” donors to developing countries!
Environmental contamination by PBDEs in e-waste
Case study: Guiyu
Guiyu is the e-waste recycling capital of the world! It is a city in the Guangdhong region of China with a population of 150,000, of which most are immigrants. About 80% of the families have members who are engaged in e-waste recycling operations. The village processes over 1.7 million tonnes of e-waste per year. These operations are of a primitive nature and include, (i) stripping of metals in open-pit acid baths to recover precious metals such as silver, copper and platinum, (ii) removing electronic components from printed circuit-boards by heating over a grill using honeycombed coal blocks (coal mixed with river sediment which is contaminated), (iii) chipping and melting plastics, (iv) burning cables to recover metals and also burning unwanted materials in open air, (v) disposing unsalvageable materials in the fields and river banks (vi) refilling of toner cartridge, and (vii) dismantling electronic equipment. Workers, often including children, carry out these activities without using goggles, masks or gloves. These crude recycling techniques have resulted in widespread environmental contamination and health problems to the workers.
During the combustion of e-waste, PBDEs are dispersed in the air via dust, providing a major exposure pathway for humans through inhalation, ingestion and skin absorption. Concentrations of total PBDEs of 16,575 pg/m3 are reported in air samples from Guiyu, about 300 times higher than in nearby Hong Kong.
Waters and aquatic systems
PBDEs can enter aquatic systems via leaching from dumpsites of processed or unprocessed e-waste. Further, the disposal of acid-waste into waters or on to soil, as well as dissolution of airborne toxicants result in contamination of aquatic systems. As these contaminants enter the food chain, diet is an important pathway of human exposure to PBDEs. Elevated levels of PBDEs are reported in carp from the Nanyang river near Guiyu (766 ng /g, fresh wt.). Sediment from the same river was also found to have high concentrations (up to 16,000 ng/g fresh wt.) of PBDEs.
Soils and terrestrial environments
Soils from a site where acid leaching was used to recover precious metals contained high levels of PBDEs (2720 - 4250 ng/g). High concentrations of PBDEs (up to 9156 ng/g) are reported from farmland soils 2 km away from an e-waste recycling facility and in plants and snails from Guiyu and the surrounding areas.
Humans and human dietary exposure
Workers at an e-waste recycling facility in Guiyu and residents of Guiyu had median blood serum PBDE concentrations of 126 ng/L and 35 ng/L respectively, while the referents from a nearby town had levels of just 10 ng/L.
Alarmingly high levels of PBDEs are reported in food samples originating from around the e-waste recycling site. The levels in chicken meat, eggs and liver and duck meat and liver were among the highest reported to date. High levels were also reported in fish. Taking all analyzed foodstuffs into account, the estimated median PBDE exposure via diet was 109.8 ng/kg bw/day for adults and 432.9 ng/kg bw/day for children. High-end estimates of exposure for children exceeded the U.S. Environmental Protection Agency's maximum acceptable oral dose (RfD). Although dietary exposure remains the principal exposure pathway in most circumstances, exposure via ingestion of contaminated dust at e-waste recycling sites is also significant.
It is also of great concern that other toxic organic pollutants such as polycyclic aromatic hydrocarbons (PAHs), polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are generated during the open burning of e-waste. Elevated levels of these pollutants are reported in dust, air, soil, vegetation, aquatic organisms and humans from locations in the vicinity of these e-waste recycling facilities.
The re-exportation of contaminants associated with e-waste: The other hidden flow
The primitive process by which e-waste is recycled in Guiyu has resulted in contamination of the entire region. Therefore, goods that are manufactured in e-waste processing regions could contain elevated levels of PBDEs and other e-waste associated contaminants. High levels of brominated flame retardants have been reported in children's toys exported from China. Although the authors do not link the source of this contaminant to e-waste, it is not inconceivable that recycled material from e-waste (containing PBDEs) has been used in the manufacture of these products. Hence, the risk of re-exportation of e-waste contaminants is a very real problem.
E-waste is a significant global environment and health issue. Further to occupational and direct local exposure, as e-waste impacts on the environment-to-food chain, widespread exposure of the general population to toxic substances occurs. Further, many negative health effects associated with e-waste have implications for generations to come. Hence, new approaches for control, management and reduction of e-waste output and burden is an urgent priority.
Professor Stuart Harrad, Division of Environmental Health & Risk Assessment, University of Birmingham, UK, for his critical comments on the document.
|A stroll through the streets of Guiyu: e-waste being collected at street corners; Sorting of e-waste; Transportation of e-waste; Open burning of e-waste; Children at work|