Title: Review of case studies on the human and environmental risk assessment of chemical mixtures
Publisher: Publications Office of the European Union
Publication Year: 2016
JRC N°: JRC102111
ISBN: 978-92-79-59146-4
ISSN: 1831-9424
Other Identifiers: EUR 27968
OP LB-NA-27968-EN-N
URI: http://publications.jrc.ec.europa.eu/repository/handle/JRC102111
DOI: 10.2788/272583
Type: EUR - Scientific and Technical Research Reports
Abstract: Humans and wildlife can be exposed to an infinite number of different combinations of chemicals in mixtures via food, consumer products and the environment, which might impact health. The number of chemicals and composition of chemical mixtures one might be exposed to is often unknown and changing over time. To gain further insight into the current practices and limitations, published peer reviewed literature was searched for case studies showing risk assessments for chemical mixtures. The aim was to find examples of mixture assessments in order to identify chemical mixtures of potential concern, methodologies used, factors hampering mixture risk assessments, data gaps, and future perspectives. Twenty-one case studies were identified, which included human and environmental risk assessments. Several compound classes and environmental media were covered, i.e. pesticides, phthalates, parabens, PBDEs, pharmaceuticals, food contact materials, dioxin-like compounds, anti-androgenic chemicals, contaminants in breast milk, mixtures of contaminants in surface water, ground water and drinking water, and indoor air. However, the selection of chemical classes is not necessarily representative as many compounds groups have not been covered. The selection of these chemical classes is often based on data availability, recent concerns about certain chemical classes or legislative requirements. Several of the case studies revealed a concern due to combined exposure for certain chemical classes especially when considering specific vulnerable population groups. This is very relevant information, but needs to be interpreted with caution, considering the related assumptions, model parameters and related uncertainties. Several parameters that could lead to an over- or underestimation of risks were identified. However, there is clear evidence that chemicals need to be further addressed not only in single substance risk assessment and that mixtures should be considered also across chemical classes and legislative sectors. Furthermore, several issues hampering mixture risk assessments were identified. In order to perform a mixture risk assessment, the composition of the mixture in terms of chemical components and their concentrations need to be known, and relevant information on their uptake and toxicity are required. Exposure data are often lacking and need to be estimated based on production and use/consumption information. Also relevant toxicity data are not always available. Toxicity data gaps can be filled e.g. using the Threshold of Toxicological Concern approach. Reference values used in single substance risk assessments can be found for several chemical classes, however, they are usually derived based on the lowest endpoint. If a refined toxicity assessment of a mixture for a specific effect/cumulative assessment group is envisaged, this is often hampered by a lack of specific toxicity and mode of action information. In all case studies, concentration addition based assessments were made, mainly applying the Hazard Index. To further characterise the drivers of the mixture risk, the maximum cumulative ratio was calculated in several case studies. This showed that the scientific methodologies to address mixtures are mostly agreed and lead to reasonable predictions. However, especially for some groups of compounds that are designed as active substances, it cannot be excluded that interactions appear and they should therefore be addressed on a case-by-case basis. Most of the mixtures addressed in the identified case studies examined specific chemical groups. Only few of them looked at mixtures comprising chemicals regulated under different legislative frameworks. The examples indicated that there is evidence for combined exposure to chemicals regulated under different legislation as well as evidence that such chemicals can elicit similar effects or have a similar mode of action. A mixture risk assessment across regulatory sectors should therefore be further investigated.
JRC Directorate:Institute for Health and Consumer Protection Historical Collection

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