Metal substances are considered as chemicals and are covered by chemicals management regulations. These regulations include those that classify chemical substances based on intrinsic hazardous properties, and those that assess risks to humans and the environment, using exposure profiles and dose-response evaluation in addition to hazard classification. Most chemicals management regulations were originally designed for assessment and management of synthetic organic chemicals. Because of this, characteristics of metal substances are often not considered, which can lead to under- or over-estimation of hazards and risks. In order to ensure appropriate and proportionate protection of human health and the environment, it is necessary that metal substances specificities are considered in assessments, and that metal-specific tools and guidelines are used when available.
There are important factors that need to be taken into account when assessing metal substances for hazard and risk assessment, which in some cases are very different from how organic chemicals are assessed. Many metal substances are essential for life, and those that are not essential can sometimes compete with the essential elements in organisms to cause adverse effects. Essentiality means that there are optimal doses that need to be present in order for the organism to be healthy and too little or too much of the metal will cause toxicity.
Metal substances are also naturally occurring and environmental conditions influence the ability of organisms to absorb the metal substances, mainly because different conditions can influence the form in which the metal is present in the environment. This also affects toxicity, as toxic effects are dependent on the absorption of the metal substance. In addition, if the metal substances are naturally found in the environment then the organisms may have the ability to tolerate the metal substance (e.g. sequestration). Finally, persistency needs to be treated differently for metal substances as metal substances may be converted in the environment in which they are present by transforming from one form to another, depending on the environmental conditions, but the metal ion itself is persistent and cannot be degraded as an element.
Tools and guidelines have been developed to enable regulators and stakeholders to deal with these metal-specific aspects in hazard identification and risk assessments, some of which have been incorporated into guidelines and regulations at local, regional, and international levels (e.g. EU, US, OECD).Tools and guidelines are compiled in this Toolbox, which is available to regulators and stakeholders to provide further insights and details to be taken into account when assessing metal substances. The objective of this toolbox is on one hand to explain in general terms what makes inorganic metal substances so different from organic compounds and on the other hand compile and provide guidance and tools specific to metal substances in order to facilitate compliance dossiers.