Chemicals are an essential part of our daily lives. They are used to produce consumer goods, to protect or restore our health and to boost food production, to name but a few examples — and they are also involved in a growing range of environmental technologies. Europe's chemical and associated industries have developed rapidly in recent decades, making a significant contribution to Europe's economy and to the global trade in chemicals. Whilst synthetic chemicals clearly bring important benefits to society, some of them are hazardous, raising concerns for human health and the environment depending on their pattern of use and the potential for exposure. Certain types of naturally occurring chemicals, such as metals, can also be hazardous. Emissions of hazardous substances to the environment can occur at every stage of their life cycle, from production, processing, manufacturing and use in downstream production sectors or by the general public to their eventual disposal. Emissions arise from a wide range of land-based and marine sources, including agriculture and aquaculture, industry, oil exploration and mining, transport, shipping and waste disposal, as well as our own homes. In addition, concern regarding chemical contamination arising from the exploitation of shale gas has grown recently. Hazardous substances in water affect aquatic life… Hazardous substances are emitted to water bodies both directly and indirectly through a range of diffuse and point source pathways. The presence of hazardous substances in fresh and marine waters and associated biota and sediment is documented by various information sources, including national monitoring programmes, monitoring initiatives undertaken by the Joint Research Centre (JRC), reporting under the Water Framework Directive (WFD), international marine conventions (e.g. HELCOM and OSPAR) and European research studies. These substances comprise a wide range of industrial and household chemicals, metals, pesticides and pharmaceuticals. Hazardous substances can have detrimental effects on aquatic biota at molecular, cellular, tissue, organ and ecosystem level. Substances with endocrine‑disrupting properties, for example, have been shown to impair reproduction in fish and shellfish in Europe, raising concerns for fertility and population survival. The impact of organochlorines upon sea birds and marine mammals is also well documented, as is the toxicity of metals and pesticides to freshwater biota. From a socio‑economic point of view, such impacts diminish the services provided by aquatic ecosystems, and consequently the revenue that can be derived from them. …and can pose risks to human health Human exposure to man-made chemicals has been implicated in a range of chronic diseases, including cancer as well as reproductive and developmental impairment. Exposure to toxic chemicals can occur via inhalation, ingestion and direct contact with skin, although the understanding of the relative risk posed by each of these exposure routes remains incomplete. However, exposure can be linked to the presence of hazardous substances in water, through the ingestion of contaminated drinking water and the consumption of contaminated freshwater fish and seafood. The exceedance of regulatory levels in seafood is documented for several hazardous substances in the seas around Europe. In addition, whilst human exposure to mercury in the Arctic, in part through the consumption of marine food, has declined, concentrations in the blood of more than 75 % of women sampled in Greenland exceed US guideline levels. Alongside concerns about exposure to individual substances, awareness is growing with regard to the importance of mixtures of several chemicals, as found in the more polluted water bodies of Europe. Laboratory studies have shown that the combined effects of chemicals upon aquatic life can be additive — resulting in observable detrimental effects for combinations of chemicals even if these are present, individually, at levels below which any adverse effects can be detected. Such concerns also extend to potential effects arising from human exposure to a mixture of chemicals via various pathways, including water. Biological effects‑directed measurements have proved to be effective in addressing the problems of complex chemical mixtures in European water bodies. In addition to the potential for adverse impacts upon human and ecosystem health, the presence of hazardous substances in drinking water supplies requires their removal. Alternatively, where the level of treatment involved is so high as to be uneconomic, a supply can be decommissioned. In both cases, significant costs are incurred. A key measure for reducing the level of purification required for Europe's drinking water is the establishment of safeguard or protection zones around the source. The creation of such zones, recognised in the WFD legislation, must be associated with regulatory powers to control polluting activities. Legislation designed to protect Europe's waters… The implementation of more established legislation related to chemicals has produced positive outcomes. Abatement measures established under the Integrated Pollution Prevention and Control (IPPC) Directive, for example, have contributed to a decline in metal emissions to water and air, whilst legislation relating to the production, use and disposal of polychlorinated biphenyls (PCBs) has resulted in declines in concentrations found in marine biota. A similar outcome has resulted from the banning of tributyltin (TBT) in anti‑fouling paints due to its endocrine-disrupting impacts on marine invertebrates, although high levels in marine sediments can still be observed in certain locations. Europe has also introduced a range of relatively recent legislation to address the use of chemicals and their emissions to the environment, including water. The Regulation on the Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH), designed to improve the protection of human health and the environment from the risks posed by chemicals, has a key role to play in this respect. REACH attributes greater responsibility to industry with regard to managing these risks and providing safety information on substances used. The Regulation also calls for the progressive substitution of the most dangerous chemicals once suitable alternatives have been identified. The chemical quality of Europe's surface waters is primarily addressed by the recently adopted Environmental Quality Standards Directive (EQSD). This WFD 'daughter' directive defines concentration limits for pollutants of EU-wide relevance known as priority substances (PSs). The limits are defined both in terms of annual average and maximum allowable concentrations, with the former protecting against long-term chronic pollution problems and the latter against short‑term acute pollution. Some of these pollutants have been designated as priority hazardous substances (PHSs) due to their toxicity, their persistence in the environment and their bioaccumulation in plant and animal tissues. The EQSD requires cessation or phase-out of discharges, emissions and losses of PHSs. For any substance identified as being of concern at local, river basin or national level, but not as a PS or PHS at EU level, standards have to be set at national level. Compliance with this requirement is critical. …is facing new challenges Some recent information with respect to the chemical status of Europe's surface water bodies is available within the WFD river basin management plans (RBMPs) which indicate, in general terms, that a variety of hazardous substances pose a threat to good chemical status in Europe. These include certain substances, for example mercury, TBT and polyaromatic hydrocarbons (PAHs), which can be described as persistent, bioaccumulative and toxic and which occur widely in the environment. Although regulation has led to documented reductions in the emissions of such substances to air and water (indeed, the presence of many is a legacy of past use), their persistence and ubiquity, particularly in sediment and biota, mean that they continue to pose a risk to aquatic environments even at sites far from human activity. The presence of these substances can cause widespread failure to achieve good chemical status under the WFD despite, in some cases, the absence of any significant risk from other types of substances. Some hazardous substances are hydrophobic and tend to accumulate in sediment and biota, with the result that their concentrations in these matrices are likely to be higher and, therefore, more detectable and measurable than in water. If measurements are made in the water column, the risk to the aquatic environment may be underestimated, and if different matrices are used in different locations and across different Member States, the results may not be directly comparable. A harmonisation at EU level is, therefore, desirable. For some pollutants, awareness and a currently incomplete understanding of potential effects have developed only recently. These emerging pollutants include substances that have existed for some time, such as pharmaceuticals and personal care products, but also relatively new substances, such as nanomaterials. Their inclusion in routine monitoring programmes has so far been limited, making it difficult to robustly assess the risks to the environment and human health, and thus to justify regulation and better monitoring. Targeted monitoring of selected emerging pollutants across the EU would be desirable to ensure timely awareness of potentially problematic substances that might need to be regulated. This monitoring should be supported by European research studies. The question of hazardous substances in Europe's fresh and marine waters is a complex issue, and climate change will add a further layer of complexity. In the absence of appropriately strong measures, this phenomenon is likely to adversely affect chemical water quality over the coming decades. In regions where more intense rainfall is expected, the frequency and severity of polluted urban storm flows is predicted to increase, whilst the flushing to water of agricultural pollutants, including pesticides and veterinary medicines, may be exacerbated. Hotter, drier summers and increasingly severe and frequent droughts will deplete river flows, reducing contaminant dilution capacity and leading to elevated concentrations of hazardous substances. Rising water temperatures and other stressors associated with climate change may interact with hazardous substances to impact the immune system health of aquatic organisms. Ocean acidification, driven by increasing atmospheric carbon dioxide (CO2), may change the speciation of metals in seawater and, therefore, their interaction with marine organisms. In addition, coastal erosion — likely to be intensified by climate change — may lead to the exposure of historical landfill sites along the coastlines of Europe, releasing hazardous substances to coastal waters. Effective measures exist… A range of measures can be implemented to reduce the emission of hazardous substances to water. It encompasses product substitution, restrictions on marketing and use, requirements to demonstrate the implementation of clean production processes and best available techniques in applications for industrial permits, fiscal instruments, the setting of emissions and environmental quality standards, and action to raise public awareness. Whilst controls 'at source' are desirable, it is very likely that other measures to attenuate the emission of hazardous substances to water will remain essential. Such measures include advanced wastewater treatment, urban stormwater controls and specific agri-environmental practices such as riparian buffer strips. Reducing emissions of hazardous substances has been shown to yield economic and societal benefits. …but they rely on sound information It is not practical or affordable to sample and analyse at sufficient spatial and temporal resolution for hundreds of individual chemicals within fresh and marine waters, including aquatic biota and sediments. However, the focus upon a few pre‑selected priority substances bears a strong risk of missing other problematic substances. In addition, such an approach disregards the effects of chemical mixtures. To address these issues, recent European research studies have led to the development and testing of new assessment and modelling tools that help to link chemical contamination with observed deterioration of ecological quality. Such tools include approaches to evaluate existing chemical and biological monitoring data, together with site-specific experimental techniques to establish cause-effect relationships. Further development of biological effects tools integrated with analytical chemistry is desirable and could contribute, in due course, to the identification of substances associated with risks, in the wider context of the update of the WFD Article 5 'pressures and impacts' analysis. European research funds can play an important role in the further development of these tools. For many hazardous substances, information on industrial emissions to water must be reported under the European Pollutant Release and Transfer Register (E-PRTR). To date, however, reporting under E-PRTR is incomplete as to the spatial extent and temporal resolution of data describing emissions to water — markedly so, for some substances. It is important not only to overcome this limitation in the reporting, but also to improve the quantitative understanding of the sources, emissions and pathways of all hazardous substances significantly. Advances in this area will facilitate the identification of appropriate measures to address chemical pollution of aquatic environments. Chemicals should be produced and used more sustainably Despite the comprehensive suite of legislation now implemented throughout Europe, the ubiquitous use of chemicals in society and their continuous release represent a major challenge in terms of the protection of aquatic ecosystems and human health. Efforts to promote a more sustainable consumption and production of chemicals are needed. They are likely to require a mix of policy responses, including regulation, economic incentives and information-based instruments. Implementing a more sustainable approach to the consumption and production of chemicals would not only benefit Europe's environment but also reduce the detrimental effects arising in other parts of the world as a result of the growing proportion of goods imported to Europe. To help achieve a more sustainable production of chemicals, wider implementation of 'green chemistry' is required. This approach involves developing new processes and technologies that maintain the quality of a product but reduce or eliminate the use and generation of hazardous substances. The adoption of sustainable, green chemistry techniques has been shown to generate financial benefits and hence provide competitive advantage. Currently, however, there is no comprehensive EU legislation on sustainable chemistry in place.