By Sally Gaw
Emerging organic contaminants are a burgeoning and extremely diverse class of contaminants that are not routinely monitored and that have the potential to have adverse ecological and human health effects.
Emerging organic contaminants (EOCs) include both naturally occurring and synthetic chemicals. Many of these contaminants may have been present in the environment for a long time but are only now have they become detectable due to advances in analytical chemistry. EOCs include active ingredients in personal care and domestic cleaning products, pesticides, plasticisers, pharmaceuticals, steroid hormones excreted by humans and animals, surfactants and veterinary medicines. Many EOCs are everyday chemicals in widespread use in consumer products. Much research is being devoted internationally to understanding the sources, environmental fate and adverse effects of EOCs.
The contaminants can enter surface and groundwater through a range of different pathways. Wastewater discharges are recognised as a major source of EOCs into aquatic ecosystems. In urban areas other potential sources include stormwater, sewer overflows, leachate from landfills and re-use of wastewater for irrigation. Rural sources include runoff from farmland, disposal of animal waste, septic tank effluents and the use of veterinary medicines in aquaculture.
The environmental fate of EOCs tends to be contaminant-specific, depending on the composition of the contaminant and in some cases the concentration and the presence of other contaminants. Potential removal pathways include photodegradation, biodegradation and sorption. Sediments can act as a sink from which EOCs can be later released. Some EOCs can bioaccumulate in aquatic organisms, however the mechanisms of uptake are not well understood. EOCs are not readily removed by conventional wastewater treatment processes as they tend to be water soluble. And while many EOCs degrade quickly in the environment, ongoing discharges into waterbodies can result in environmental concentrations and hence exposure of aquatic organisms remaining relatively constant.
The majority of EOCs are typically present in aquatic ecosystems at parts-per-trillion to parts-per-billion concentrations. Despite these low concentrations, a range of adverse effects have been reported in wildlife including endocrine disruption effects on growth and reproduction, genotoxicity, organ damage, and changes in behaviour. Exposure to environmentally relevant concentrations of ethinylestradiol an active ingredient in contraceptive pills can cause reproductive effects and behavioural changes in fish. Similarly the non-steroidal anti-inflammatory diclofenac can cause kidney damage in fish at concentrations routinely measured in wastewaters in North America and Europe. The presence of antibiotics and anti-microbial compounds can lead to the development of antibiotic resistance in pathogenic bacteria creating serious risks for human health. Exposure to EOCs can also alter the nutrient processing capacity and natural food web structure of aquatic ecosystems. For example the anti-microbial compound triclosan can alter the species diversity of algal communities. In most aquatic ecosystems, EOCs will be present as mixtures alongside other environmental stressors. The combined effects of mixtures of EOCs and the presence of multiple stressors on aquatic organisms are poorly understood. EOCs may be the tipping point for endangered species and aquatic food chains.
There is very limited data available on EOCs in New Zealand. What we do have indicate that EOCs are present in wastewater and environmental matrices at comparable concentrations to those measured internationally. The sensitivity of New Zealand’s unique aquatic fauna to EOCs is unknown. Further data will be needed to understand and reduce the impacts of EOCs on freshwater ecosystems in New Zealand including identification of the key EOCs of concern. Risks specific to New Zealand due to usage patterns or sensitivity of aquatic organisms and receiving environments also need to be identified. This information will underpin future policy and regulatory decision making for EOCs to protect New Zealand’s waterways.
Dr Sally Gaw is a Senior Lecturer in Environmental Chemistry and Director of the Environmental Science Programme at the University of Canterbury.
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