Antibiotics are found globally in the environment at trace levels due to their extensive consumption, which raises concerns about the effects they can have on non-target organisms, especially environmental micro-organisms. So far the majority of studies have focused on different aspects of antibiotic resistance or on analyzing the occurrence, fate, and removal of antibiotics from hospital and municipal wastewaters. Little attention has been paid to ecotoxicological effects of antibiotics on aquatic micro-organisms although they play a critical role in most ecosystems and they are potentially sensitive to these substances. Here we review the current state of research on the toxicological impacts of antibiotics to aquatic micro-organisms, including proteobacteria, cyanobacteria, algae and bacteria commonly present in biological wastewater treatment processes. We focus on antibiotics that are poorly removed during wastewater treatment and thus end up in surface waters. We critically discuss and compare the available analytical methods and test organisms based on effect concentrations and identify the knowledge gaps and future challenges. We conclude that, in general, cyanobacteria and ammonium oxidizing bacteria are the most sensitive micro-organisms to antibiotics. It is important to include chronic tests in ecotoxicological assessment, because acute tests are not always appropriate in case of low sensitivity (for example for proteobacteria). However, the issue of rapid development of antibiotic resistance should be regarded in chronic testing. Furthermore, the application of other species of bacteria and endpoints should be considered in the future, not forgetting the mixture effect and bacterial community studies. Due to differences in the sensitivity of different test organisms to individual antibiotic substances, the application of several bioassays with varying test organisms would provide more comprehensive data for the risk assessment of antibiotics. Regardless of the growing concerns related to antibiotics in the environment, there are still evident knowledge gaps related to antibiotics, as there is only limited or no ecotoxicological data on many potentially harmful antibiotics.

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The passive samplers collected bioavailable and bioaccessible chemicals from the WWTP sludge samples.• The sampler extracts were acutely and chronically toxic to water flea. • The sampler extracts were cytotoxic and genotoxic.• The sludge treatment such as composting and digesting diminished the toxicity. • Effect-based methods should be part of the risk assessment of sludge recycling.

Sediment from a log pond located in south Finland contained 15 000 to 50 000 mg/kg dry weight of C10–C40 hydrocarbons. It was unclear whether they originated from the hydraulic fluid of the log hoist or the wood extractives. In the present study, methods of effect‐directed analysis were used for the identification of toxicants. A combination of fractionation, biotesting, and chemical analyses revealed that the key toxicant of log pond sediment was retene, a dialkyl‐substituted phenanthrene derived from wood resin acids. In addition, the most toxic fraction included 3 other wood‐originated diterpenic compounds. Typical wood extractives such as sesquiterpenes and odd–carbon number alkanes in the range C21–C33 were identified in the fraction, which showed minor genotoxic potency. The most polar fraction contained triterpenes and showed estrogenic activity. No evidence for the presence of hydraulic fluid in sediment was found. The study also indicated that in cases where the organic matter content of sediment or soil is high, using the results of standard mineral oil analysis in risk management can lead to incorrect actions because standard methods do not differentiate petroleum hydrocarbons from biogenic hydrocarbons. Environ Toxicol Chem 2019;9999:1–11. © 2019 SETAC