Historically, many additives and catalysts used in plastics were based on compounds of toxic metals (and metalloids), like arsenic, cadmium, chromium(VI), and lead. Despite subsequent restrictions, hazardous additives remain in plastics in societal circulation because of the pervasiveness of many products and the more general contamination of recycled goods. However, little is understood about their presence and impacts in the environment, with most studies focusing on the role of plastics in acquiring metals from their surroundings through, for example, adsorption. Accordingly, this paper provides a review of the uses of hazardous, metal-based additives in plastics, the relevant European regulations that have been introduced to restrict or prohibit usage in various sectors, and the likely environmental impacts of hazardous additives once plastics are lost in nature. Examination of the literature reveals widespread occurrence of hazardous metals in environmental plastics, with impacts ranging from contamination of the waste stream to increasing the density and settling rates of material in aquatic systems. A potential concern from an ecotoxicological perspective is the diffusion of metals from the matrix of micro- and nanoplastics under certain physico-chemical conditions, and especially favorable here are the acidic environments encountered in the digestive tract of many animals (birds, fish, mammals) that inadvertently consume plastics. For instance, in vitro studies have shown that the mobilization of Cd and Pb from historical microplastics can greatly exceed concentrations deemed to be safe according to migration limits specified by the current European Toy Safety Directive (17 mg kg^-1 and 23 mg kg^-1, respectively). When compared with concentrations of metals typically adsorbed to plastics from the environment, the risks from pervasive, historical additives are far more significant.

Environmental context. Antimony first attracted public attention in the mid-1990s amid claims that it was involved in Sudden Infant Death Syndrome. A substantial number of papers have now been published on the element and its behaviour in the natural environment. However, many key aspects of the environmental chemistry of antimony remain poorly understood. These include critical areas such as its ecotoxicology, its global cycling through different environmental compartments, and what chemical form it takes in different environments. More focussed research would help the situation. The present review highlights several areas of environmental antimony chemistry that urgently need to be addressed. The objective of the present article is to present a critical overview of issues related to the current state of knowledge on the behaviour of antimony in the environment. It makes no attempt to systematically review all published data. However, it does provide a list of the main published reviews on antimony and identifies subjects where systematic reviews are needed. Areas where our knowledge is strong – and the corresponding gaps – in subjects ranging from total concentrations and speciation in the various environmental compartments, to ecotoxicity, to cycling between compartments, are discussed, along with the underlying research. Determining total antimony no longer poses a problem for most environmental samples but speciation measurements remain challenging throughout the process, from sampling to analysis. This means that the analytical tools still need to be improved but experience shows that, to be useful in practice, this should be directly driven by the requirements of laboratory and field measurements. Many different issues can be identified where further research is required, both in the laboratory and in the field, the most urgently needed studies probably being: (i) long-term spatial and temporal studies in the different environmental compartments in order to collect the data needed to establish a global biogeochemical cycle; (ii) laboratory studies of antimony interactions with potential natural binders; (iii) reliable ecotoxicological studies.

Environmental context: Microplastics, either purposefully manufactured or formed by fragmentation of discarded ‘end-of-life’ macroplastic items, are accumulating in environmental compartments. As more and more data are collected on microplastics in the environment, discussion of two issues has become indispensable: (i) how reliable are the results in terms of the inherent capabilities and limitations of current methods used for sampling, counting and measuring microplastic particles; and (ii) how can the fate of microplastics be understood in the context of natural particles and colloids? A first important step in evaluating the impact of microplastic pollution in natural systems is assessing the reliability of the results obtained according to the inherent capabilities and limitations of the methods used for sampling, counting and measuring microplastic particles. This study, based on the critical reading of 55 studies containing quantitative microplastic data in waters and sediments, is an attempt to analyse these issues in the light of existing knowledge in the field of natural colloid studies. Existing results are highly dependent on the sampling and methodological procedure chosen and are essentially descriptive. Moreover, often they lack standardisation and adequate reporting of basic information such as the meaning of the size parameter measured. Colloid theory may provide the theoretical background needed to explain microplastic behaviour or, at least, to identify the parameters (e.g. density, surface characteristics, shape) that need to be known in order to gain a predictive knowledge of the subject. They are introduced and discussed. Finally, microplastics are not alone in environmental compartments. For this reason, when possible, published microplastic particle size distributions in natural waters have been quantitatively situated in the context of natural particles.

The current socio-economic, environmental and public health challenges that countries are facing clearly need common-defined strategies to inform and support our transition to a sustainable economy. Here, the technology-critical elements (which includes Ga, Ge, In, Te, Nb, Ta, Tl, the Platinum Group Elements and most of the rare-earth elements) are of great relevance in the development of emerging key technologies—including renewable energy, energy efficiency, electronics or the aerospace industry. In this context, the increasing use of technology-critical elements (TCEs) and associated environmental impacts (from mining to end-of-life waste products) is not restricted to a national level but covers most likely a global scale. Accordingly, the European COST Action TD1407: Network on Technology-Critical Elements (NOTICE)—from environmental processes to human health threats, has an overall objective for creating a network of scientists and practitioners interested in TCEs, from the evaluation of their environmental processes to understanding potential human health threats, with the aim of defining the current state of knowledge and gaps, proposing priority research lines/activities and acting as a platform for new collaborations and joint research projects. The Action is focused on three major scientific areas: (i) analytical chemistry, (ii) environmental biogeochemistry and (iii) human exposure and (eco)-toxicology.

Over the last 30 years, bottled water has gained in popularity reaching high sales world-wide. Most of this water is sold in polyethylene terephthalate (PET) bottles. About 15 years ago, the presence of antimony in water in those PET bottles raised concerns and studies on the subject have been regularly published since then. This review aims to evaluate whether the use of good analytical practices and the correct design of these studies support the accepted facts (i.e., PET is the origin of antimony presence in bottled waters, antimony concentrations are usually below regulated values, temperature increasing favours antimony leaching). The detailed analysis of published data has confirmed these facts but has also revealed frequency of faulty analytical practices and a lack of well-designed studies. A better understanding of the structure of PET polymer in the bottles, coupled with statistically-robust antimony release experiments, is required to progress in the field.