Biomethylation of metals and metalloids is a well-known process ubiquitously occurring in the environment, which leads to the formation of chemical species with significantly higher mobility and altered toxicity. The transfer of methyl groups is established not only under anaerobic conditions, but also within aerobic milieus and has been described in natural systems for arsenic, cadmium, germanium, mercury, sulfur, antimony, selenium, tin, tellurium, and lead as well as for bismuth, gold, chromium, palladium, platinum, and thallium under laboratory conditions. Abundant literature is available to describe analysis, genesis, and environmental distribution of organometal(loids) in the environment. Thus, it became widely known that these compounds exhibit particular physicochemical properties like volatility (e.g., peralkylated species) or amphiphilicity (e.g., partly alkylated species) leading to increased mobility within the ecosphere as well as inside organisms (e.g., membrane diffusion), and therefore attracting the attention of environmentalists and toxicologists. Although it has been widely recognized that the toxic potential of organometal(loid) compounds may be comparable or even higher than that of inorganic species of the respective elements (e.g., arsenic or mercury), relevant data for the evaluation of the health impact of many environmental organometal(loids) are still scarce (e.g., bismuth, selenium, and tellurium). In this respect, it has also to be considered that humans are not only exposed to these compounds from the environment via inhalation and ingestion, but may also be able to generate these species by endogenous enzymes or/and biomethylation in the colon.

To investigate the toxicity of organometal(loid) compounds, it is crucial to combine the toxicological testing with analytical methods because organometal(loids) can be biomethylated intracellularly and thus can affect human health. This special issue is aimed at meeting these requirements and getting more information about the toxicological behaviour of many so far unknown organometal(loid) species. Potential topics include, but are not limited to:

• Toxicity of compounds containing at least one metal(loid)-carbon bond. Although the most important members of this group may be alkylated (especially methylated) species, also others like carbonyls will be welcomed
• Elements just emerging like antimony, bismuth, or tellurium in addition to often discussed ones like arsenic, mercury, tin, and lead
• Data concerning acutely toxic, geno- and neurotoxic effects observed in cellular and animal experiments
• Processes of metabolic alkylation and dealkylation in humans and animals
• Epidemiological studies which are linked to analytical measurements of arsenic species in urine or blood
• Mechanistic studies regarding cellular pathways of metal(loid) toxicity