In Europe and North America, there has been a gradual decrease in common environmental contaminants (heavy metals such as lead, cadmium; persistent organic pollutants such as DDT, Dioxin, PAH’s) in the environment. This improvement is largely due to a concerted effort of stricter regulations with improved monitoring, cleaner industrial processes and increased public awareness. Common environmental contaminants, however, remain a public health concern in developing countries and newly industrialised countries.
As we experience a decline in the levels and point sources of common chemicals, the focus has now been on the chemicals which were previously not considered as contaminants. They are not geogenic or air-born but are mainly synthetic by nature and produced to offer a range of societal benefits. Unlike common contaminants, ‘emerging chemical contaminants’ mostly find their way to the environment via diffuse sources i.e. domestic, commercial, and industrial uses. In addition, the development of more sensitive and new analytical capabilities that allows scientist to identify contaminants which are typically present in ultra-low concentrations (parts per billion to parts per trillion). The low concentrations combined with a lack of toxicological evidence make hazard characterisation technically challenging and thus the regulatory standards, where available, tend to be less rigorous and are advisory rather than prescriptive. In some cases (e.g. flame retardants) there are difficulties in identifying safer alternatives even when new evidence emerges about the health risk from the currently used materials.
Some examples of emerging contaminants include: perfluorocarbons ((e.g. perfluorooctane sulfonate (PFOS)), perfluorooctanoic acid (PFOA)), pesticides residues/metabolites (e.g. metaldehyde), pharmaceuticals and personal care products (e.g. steroids and antibiotics, fragrances, cosmetics), nanomaterials (e.g. buckeyballs or fullerenes; carbon nanotubes). These chemicals or their parent products are being manufactured to improve the quality and safety or to increase the efficiency in industrial processes. By nature, they are intended to last long or be resistant to microbial degradation in the environment. For example, PFCs contains only carbon and fluorine bonded together in strong carbon-fluorine bonds which made them chemically inert and thermally stable. When these chemicals (e.g. PFOS, antibiotics, steroids) are released to the public sewer system, conventional water treatment processes can do little to render them harmless and go unabated to enter the wider environment and biotic food chain as a pollutant.
Our knowledge to relate the presence of emerging chemicals in the environment with public health significance is still at its infancy. Bioassays with animal models indicate the potential for toxicity to humans if exposed to a very high doses but such high dose exposure is unrealistic when compared to typical environmental concentrations. Uncertainty, however, remains over the potential health impacts from a low level chronic exposure due to their persistence and bioaccumulative nature. Studies with ecological receptors e.g. with fish in streams contaminated by steroids have shown evidence of hormone disruption. There is also concern that elevated exposure to antibiotics in water could lead to disease-resistant strains of bacteria, reducing the effectiveness of the current class of drugs. For the human population, the limited data available suggests that there is a need for more “prospective cohort” type study to characterise the association between environmental exposure to these substances, appropriate biomarkers and measurable health outcomes.
Emerging chemicals should be a source of concern to ecological and public health in all parts of the world. In this era of financial constraint and interdependent/connected economies, there is a need for shared research programme and data-sharing to enhance analytical capacity to determine their environmental occurrence, fate and transport. There is also a need for improved risk assessment tools to characterise the exposure and extrapolation of ecological risk to public health if relevant and appropriate. Regulatory policy should encompass emerging chemicals in their monitoring regime, and encourage safer alternatives, increased awareness and risk reduction programme. Societies like the SEGH can facilitate research consortia or a task force drawing from its international expertise to influence the relevant public policy and apply for research funding. Further information on emerging chemicals can be found in websites of various regulatory and public health organisations such as European Chemicals Agency, US EPA, ATSDR.
Sohel Saikat, Health Protection Agency, UK.