In the last few years there has been growing controversy over the incineration of health-care waste. Under some circumstances, including when wastes are incinerated at low temperatures or when plastics that contain polyvinyl chloride (PVC) are incinerated, dioxins and furans and other toxic air pollutants may be produced as emissions and/or in bottom or fly ash (ash that is carried by air and exhaust gases up the incinerator stack). Exposure to dioxins, furans and co-planar PCBs may lead to adverse health effects.
Dioxins, furans and co-planar PCBs are toxic substances produced as by-products of various industrial processes, including the combustion of wastes containing polyvinyl chloride (e.g., some plastics, some blood bags and fluid bags). This happens particularly when wastes are incinerated at temperatures lower than 800 degrees Celsius or when the wastes are not completely incinerated. Dioxins, furans, co-planar PCBs and other toxic air pollutants may then be produced as emissions and/or in bottom or fly ash. In some circumstances dioxins and furans can be produced under natural conditions (e.g. volcanic activity and forest fires).
Polychlorinated dibenzo-para-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and polychlorinated biphenyls (PCBs) are called dioxins, furans and co-planar PCBs, respectively. Amongst the different dioxins and furans, not all have the same toxicity; some are even harmless. Dioxins, furans and co-planar PCBs are persistent substances that do not readily break down in the environment and that bio-accumulate in the food chain. Most human exposure to dioxins, furans and co-planar PCBs is through the intake of food.
Long-term, low-level exposure of humans to dioxins and furans may lead to the impairment of the immune system, the impairment of the development of the nervous system, the endocrine system and the reproductive functions. Short-term, high-level exposure may result in skin lesions and altered liver function. Exposure of animals to dioxins has resulted in several types of cancer.
The International Agency for Research on Cancer (IARC) classifies dioxins as a "known human carcinogen". However, most of the evidence documenting the toxicity of dioxins and furans is based on studies of populations that have been exposed to high concentrations of dioxins either occupationally or through industrial accidents. There is insufficient evidence to prove that chronic low-level exposures to dioxins and furans causes cancer in humans.
WHO has established a Provisional Tolerable Monthly Intake (PTMI) for dioxins, furans, and polychlorinated biphenyls (PCBs) of 70 picograms (10-12 g) per kilogram of body weight. The PTMI is an estimate of the amount of chemical per month that can be ingested over a lifetime without appreciable health risk. Almost all exposure to dioxins and furans is through the food chain and the PTMI represents the cumulative exposure to dioxins and furans from all sources including food and water.
It has not yet been possible to estimate the worldwide burden of mortality and morbidity from exposure to dioxins and furans: the exposure and risk assessment has many uncertainties; data gaps are very large.
Additionally, the types of health effects that may result (e.g. cancer, impaired immune function) would only show up after long exposure periods and would be difficult to measure.
WHO has established tolerable intake limits for dioxins and furans, but not for emissions. The latter must be set within the national context.
A number of countries have defined emission limits that range from 0.1 ng TEQ/m3 (Toxicity Equivalence) in Europe to 0.1 ng to 5 ng TEQ/m3 in Japan, according to incinerator capacity.
Even in high temperature incinerators (>800 °C), temperatures are not uniform and dioxins and furans can form in cooler pockets or during start-up or shut-down periods. Optimization of the incineration process can reduce the formation of these substances by, for example, ensuring that incineration takes place only at temperatures above 800°C, and that flue gas temperatures in the range of 250°C to 450°C are avoided.
In the last 10 years, stricter emission standards for dioxins and furans in many countries have significantly reduced the release of these substances into the environment. In several European countries where tight emissions restrictions were adopted in the late 1980s, dioxin and furan concentrations in many types of food (including mother's milk) have decreased sharply.
The safe disposal of health-care waste generated at smaller rural clinics or larger facilities is feasible where adequate, well-operated infrastructure exists. However, the volume of waste generated within large facilities and during immunization campaigns may be difficult to dispose of safely when resources are limited. In 2001, during a measles mass immunization campaign in West Africa (covering all or part of six countries), 17 million children were vaccinated, resulting in the generation of nearly 300 metric tonnes of injection waste. Without adequate waste disposal options at both local and regional levels, this volume of waste would have been difficult to eliminate safely.
The unsafe disposal of health-care waste (for example, contaminated syringes and needles) poses public health risks. Contaminated needles and syringes represent a particular threat as the failure to dispose of them safely may lead to dangerous recycling and repackaging which lead to unsafe reuse. Contaminated injection equipment may be scavenged from waste areas and dumpsites and either be reused or sold to be used again. WHO estimated that, in 2000, contaminated injections with contaminated syringes caused:
In 2002, the results of a WHO assessment conducted in 22 developing countries showed that the proportion of health-care facilities that do not use proper waste disposal methods ranges from 18% to 64%.
In addition to the public health risks, if not managed, direct reuse of contaminated injection equipment results in occupational hazards to health workers, waste handlers and scavengers. Where waste is dumped into areas without restricted access, children may come into contact with contaminated waste and play with used needles and syringes. Epidemiological studies indicate that a person who experiences one needle stick injury from a needle used on an infected source patient has risks of 30%, 1.8%, and 0.3% respectively of becoming infected with HBV, HCV and HIV.
The management of health-care waste requires increased attention and diligence to avoid the substantial disease burden associated with poor practice, including exposure to infectious agents and toxic substances. Incinerators provide an interim solution especially for developing countries where options for waste disposal such as autoclave, shredder or microwave are limited.
Whatever the technology used, best practice must be promoted to ensure optimal operation of the system. To reduce exposure to toxic pollutants associated with the combustion process such as dioxins, furans, co-planar PCBs, nitrogen and sulphur oxides as well as particulate matter and to minimize occupational and public health risks, "best practices" for incineration must be promoted, and must include the following elements:
Management and operational problems with incinerators, including inadequate training of operators, waste segregation problems, and poor maintenance, are recognized as critical issues that should be addressed in assessment and waste management plans.
To better understand the problem of health-care waste management, WHO guidance recommends that countries conduct assessments prior to any decision as to which health-care waste-management methods be chosen. Tools are available to assist with the assessment and decision-making process so that appropriate policies lead to the choice of adapted technologies. In support of sound health-care waste management, WHO proposes to work in collaboration with countries through the following strategy:
WHO aims to promote effective non-burn technologies for the final disposal of medical wastes to avoid both the disease burden from unsafe health-care waste management and potential risks from dioxins, furans and co-planar PCBs. WHO will: