Abstract
Micro- and nanoplastics (MNPs) are widespread environmental contaminants with growing evidence of biological toxicity. While size, shape, and polymer type have traditionally dominated hazard discussions, plastic additive chemicals are increasingly recognized as key drivers of MNP toxicity[1]. Additives such as plasticizers, stabilizers, flame retardants, and colorants are intentionally added during manufacturing but are not chemically bound to the polymer, enabling their release into surrounding media, including water and biological fluids. The role of additives is complex, especially considering over 16,000 different chemicals are in use globally[2]. These vary significantly by polymer type and individual consumer product, and many lack comprehensive toxicological data. Additionally, non-intentionally added substances (NIAS), such as production chemicals and degradation by-products, also contribute to the chemical profile and potential toxicity of MNPs. The leaching of these substances is influenced by environmental conditions and particle surface area, which is particularly relevant for nanoplastics[3]. Despite these concerns, most MNP hazard assessments rely on poorly characterized or additive-free test materials, limiting ecological and regulatory relevance. There is a critical need for test and reference materials that reflect real-world plastic products, both chemically and physically[4]. Car tyres exemplify the issue: composed of rubber and a large number of additives, their leachates are known to be toxic[5]. Understanding whether observed toxicity originates from the particles, the leached chemicals, or both is crucial[6]. Therefore, standard methods to separate particle and chemical toxicity—such as leachate testing or chemical extraction—must be implemented in hazard assessment. Without such approaches, the true drivers of observed toxicity remain unclear. Chemical additives and NIAS are central to the hazard profile of MNPs. Future research and regulation must incorporate additive chemistry to provide accurate environmental and health risk assessments and inform effective mitigation strategies.