Hydrocarbon solvents are petrochemicals used in a wide range of industrial and consumer applications globally.These products consist of many different hydrocarbon constituents and are described as UVCB substances (substances of Unknown or Variable composition, Complex reaction products or Biological materials).They are most commonly derived from the processing of crude oil, but other varieties, such as synthetic isoparaffins and solvents derived by the Fischer-Tropsch, or Gas-to-Liquid (GTL) process, also exist.Although different solvents may share similar performance properties, their composition varies depending on the manufacturing process and they are regarded as different substances under chemical regulatory programmers.In order to assess the relative aquatic toxicity of GTL solvents compared with other hydrocarbon solvents a range of screening methods have been used.These included testing of water-accommodated fractions (WAFs) using solid-phase micro-extraction (SPME) combined with gas chromatography (GC) analysis, MICROTOXTM and DAPHTOXKIT FTM assays, and toxicity predictions using the PETROTOX model.Results were compared with compositional information for each of the substances and available experimental data from GLP compliant acute aquatic toxicity studies, conducted under OECD guidelines.The results of the screening tests suggested that acute toxicity of GTL Solvents is dependent on hydrocarbon chain length, similar to dearomatised and isoparaffinic hydrocarbon solvents.The white spirits were significantly more toxic based on screening data, which was expected based on the presence of aromatic constituents.On the basis of the experimental screening methods applied, the two most sensitive approaches for detecting toxicity of the various products are SPME-GC and the DAPHTOXKIT FTM test kit, whereas the MICROTOXTM assay is the least sensitive.The PETROTOX calculations predicted a similar relationship with chain length, but were generally more conservative than the experimental data.Overall, through the use of a range of screening methods in a weight of evidence approach, the acute aquatic toxicity of GTL solvents was successfully determined relative to other types of hydrocarbon solvents.