Current safety assessment practice is primarily based on understanding the potential risk posed by single substances rather than their "real life" combinations, thus potential combination effects might be overlooked. How can the safety of combined exposures to multiple chemicals for people and the environment be addressed?
Every day we are exposed to low levels of hundreds of different manmade chemicals present for example in our food, consumer products and the air we breathe. Our environment too is exposed to a near-infinite number of chemical mixtures derived from numerous sources.
The Joint Research Center (JRC) of the European Commission is investigating recent progress in considering combined exposures to multiple chemicals to help translate best science into best assessment practice. The latest policy brief ,Something from nothing? Ensuring the safety of chemical mixtures' puts together issues around the topic, including the specific challenges that will further inform discussions of the working group of Commission services and EU agencies on the combination effects of chemicals.
The 'Mixtures' Issue
Combined exposure to multiple chemicals can lead to adverse effects on human health or the ecosystem, even if single substances in the mixtures are below their individual safety thresholds. The assessment and management of chemical mixtures is only partly covered by current legislation, which focuses mostly on single substances. In particular, while manufactured products such as pesticide formulations or cosmetic products are covered, unintentional mixtures which are coincidentally formed such as mixtures of contaminants e.g. in indoor air, are not consistently addressed. Their composition is often unknown and changes over time, making them difficult to regulate. The assessment of unintentional mixtures is therefore usually limited to specific legislative sectors only, such as pesticide residues in food.
Current Assessment of Chemical Mixtures
Different methods are already being used to predict or assess mixture toxicity. Chemical mixtures are assessed either by testing the whole mixture (e.g. in effect-based monitoring of surface water) or by predicting the combined risk based on concentration and effect information of the individual components in the mixture (e.g. in the assessment of dioxins and dioxin-like compounds in food and feed). With a view to harmonising assessment methodology, international bodies, such as the World Health Organisation (WHO) and the Organisation for Economic Cooperation and Development (OECD) have developed guidance on the assessment of risks from combined exposure to multiple chemicals. However, there are still many gaps concerning availability and interpretation of data, and there is no harmonised assessment approach across different sectors of legislation.
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