by Mr. Andrew Strawson

A detailed assessment of the health effects of POPs is given in the Ritter report, and this presentation is based on that report.

Persistent organic pollutants (POPs) are organic compounds that, to a varying degree, resist photolytic, biological and chemical degradation. POPs are often halogenated and characterised by low water solubility and high lipid solubility, leading to their bioaccumulation in fatty tissues. They are also semi-volatile, enabling them to move long distances in the atmosphere before deposition occurs.

Humans can be exposed to POPs through diet, occupational accidents and the environment (including indoor). Exposure to POPs, either acute or chronic, can be associated with a wide range of adverse health effects, including illness and death.

Laboratory investigations and environmental impact studies in the wild have implicated POPs in endocrine disruption, reproductive and immune dysfunction, neurobehavioural and developmental disorders and cancer. More recently some POPs have also been implicated in reduced immunity in infants and children, and the concomitant increase in infection, also with developmental abnormalities, neurobehavioural impairment and cancer and tumour induction or promotion. Some POPs are also being considered as a potentially important risk factor in the etiology of human breast cancer by some authors.

It is most difficult to establish cause and effect relationships for human exposure of POPs and incident disease. Humans encounter a broad range of environmental exposures and frequently to a mixture of chemicals at any one time. Much work remains to be done on the study of the human health impact of exposure to POPs, particularly in view of the broad range of concomitant exposing experienced by humans.

The weight of scientific evidence suggests that some POPs have the potential to cause significant adverse effects to human health, at the local level, and at the regional and global levels through long range transport.

For some POPs, occupational and accidental high-level exposure is of concern for both acute and chronic worker exposure. The risk is greatest in developing countries where the use of POPs in tropical agriculture has resulted in a large number of deaths and injuries. In addition to other exposure routes, worker exposure to POPs during waste management is a significant source of occupational risk in many countries. Occupational, bystander and near-field exposure to toxic chemicals is often difficult to minimize, with obstacles to managing workplace exposure in part due to poor or non-existent training, lack of safety equipment, and sub-standard working conditions. Although there is a lack of epidemiological data, it has been shown that short-term exposure to high concentrations of certain POPs has resulted in illness and death.

Although such obvious effects are not as common in the case of exposure to lower concentrations, laboratory and field observations on animals, as well as clinical and epidemiological studies in humans, and studies on cell cultures collectively demonstrate that overexposure to certain POPs may be associated with a wide range of biological effects.

These adverse effects may include immune dysfunction, neurological deficits, reproductive anomalies, behavioural abnormalities and carcinogenesis. Some studies link dietary intake of POPs to important reductions in the lymphocyte population, while other studies suggest that children with high organochlorine dietary intake may experience rates of infection some 10-15 times higher than comparable children with lower intakes.

Researchers have suggested a relationship between exposure to some POPs and reproductive dysfunction. The developing fetus and neonate are particularly vulnerable to POPs exposure due to transplacental and lactational transfer of maternal burdens at critical periods of development.

The general conclusion is that exposure to POPs has a significant impact on human health both in the short and long term. High (over)exposures at the point of use will lead to acute effects, including death, while long term effects are likely even at lower exposure levels.