More controversy, little clarification
Authors: Carrie A Redlich
Journal: The Lancet (1998)

Concern and controversy about the effects on human health of low-level but widespread environmental exposures contiopnued to grow in 1998. New studies provided reason for both concern and reassurance regarding the effects of exposures such as air pollution, endocrine-disrupting chemicals, power lines, and landfill sites. The impact of low-level exposures on human health has proved difficult to investigate, but refined environmental epidemiological methods and mechanistic studies are providing new insights. The environmental justice movement gained momentum; further studies suggested that disadvantaged and minority communities are disproportionately exposed to hazardous substances. Much work focused on the problem of asthma in these communities. 1998 saw further research into effects on health of various constituents of air pollution (including ozone, fine particulate matter [PM2,5], larger particulates [PM10], diesel exhaust, and sulphur dioxide) adding support to a causal relationship between air pollution and various adverse health outcomes. Which constituents of air pollution are responsible for the adverse effects and how they should be regulated was a source of controversy, much of it centred around PM2,5 data. Studies of a number of different occupational and environmental exposures provided increasing evidence of a central role for reactive oxygen species in mediating injury, as well as the importance of interactions between different exposures. For example, studies suggested that diesel exhaust particles may skew the immune response towards IgE production, possibly increasing susceptibility to other environmental antigens. The carcinogenic potential of diesel fuel is also being investigated. Whether endocrine-disrupting chemicals in the environment can cause adverse effects in human beings, as has been documented in wildlife and animal studies, was an active area of research. A growing number of case-control studies of breast-cancer risk showed no significant association with plasma concentrations of endocrine-disrupting chemicals. However, animal and in-vitro studies provided further evidence that numerous natural and man-made environmental chemicals have oestrogenic activity, with the potential to cause reproductive abnormalities and alter the growth of breast-cancer cells. The question remains as to whether or not humans are exposed at sufficient doses to cause an effect. Other reproductive concerns included congenital anomalies. A recent multi-centre case-control study from five European countries found an increased risk of congenital anomalies in babies whose mothers lived close to landfill sites handling hazardous wastes. Residential magnetic-field exposure has generated much concern in the past. A well-done case-control study demonstrated that childhood leukaemia was not associated with residential magnetic-field levels. However, a recent report in The Lancet found higher systolic and diastolic blood pressure in 10 volunteers during exposure to the radio-frequency electromagnetic fields of a mobile telephone. This finding warrants further investigation. The Gulf war syndrome and its cause remain elusive. Research on another longstanding controversial environmental concern, low-level asbestos exposure, generated further data suggesting minimal risk, but these did not abate the controversy. Lead, one of the oldest, best-studied toxic environmental substances, remained an area of active research, with studies confirming that chronic low-level exposure to lead can result in hypertension. Global warming continued, the list of unconcerned scientists shrinking further. Interest in environmental exposures will continue to grow. There is a greater awareness that, although environmental health risks are generally of low magnitude and difficult to prove, they may still pose an important public health problem if large numbers of people are exposed, and if certain populations are disproportionately exposed. In the coming year, integrating environmental epidemiological and mechanistic approaches should continue to elucidate which of the many environmental exposures truly pose important human health hazards. The need for better risk assessment, and better education of the public regarding environmental risks is also being recognised.