Severity Classification of Clinical Signs and Defining the Moribund State as an Experimental Endpoint for Acute Toxicity Testing Using Japanese Medaka (Oryzias latipes)

Use of the moribund state as an endpoint for acute toxicity testing in fish is complicated by the lack of consensus about the sublethal signs that define the state or that can predict imminent death. Defining the moribund state in fish requires determination of the association between each observable sublethal sign and transition to imminent death. To establish a criterion for defining the moribund state in Japanese medaka (Oryzias latipes), we determined death/clinical-sign ratios, defined as the proportion of fish with each clinical sign that transitioned to imminent death, for 13 clinical signs observed in individually housed fish exposed to one of two typical toxicants, three pharmaceuticals, two pesticides, and one metal. Also, the time from onset of each clinical sign to transition to imminent death (referred to as the survival time) was determined by continuous monitoring. Three of the observed clinical signs-immobility, lethargy, and immobility at the surface-were found to be indicators of the moribund state, with each of these signs having a death/clinical-sign ratio of 1.0. Evaluation of the survival time after onset of the other 10 signs enabled determination of whether timely euthanasia would be appropriate, thereby providing a means of reducing the suffering of laboratory fish in the period before death. Environ Toxicol Chem 2022;41:1089-1095. © 2022 SETAC.

Species and Life-Stage Sensitivity of Chinese Rare Minnow (Gobiocypris rarus) to Chemical Exposure: A Critical Review

Chemical production and consumption in Asia are increasing at an unprecedented rate, calling for regulations on chemical management. Under the New Chemical Substance Notification in China, information on ecotoxicological effects of chemicals is mandatory for the simplified registration of chemicals with the requirement that one ecotoxicological test is conducted locally. It is now mandatory to use the native fish species Chinese rare minnow (Gobiocypris rarus). However, its chemical sensitivity compared to that of fathead minnow (Pimephales promelas) or zebrafish (Danio rerio) is still unclear. We performed a holistic literature review on toxicity data with G. rarus from 1997 to 2020. Species sensitivity among G. rarus, P. promelas, and D. rerio and life-stage sensitivity of G. rarus were systematically investigated for various chemicals using both chemical ratio distribution and probabilistic chemical toxicity distribution approaches. Comparatively, the Chinese native fish species G. rarus was more sensitive than D. rerio, particularly to metals. Juvenile and adult G. rarus were more sensitive than its larvae and embryos. The observed lower sensitivity of G. rarus embryo was likely due to the thick embryonic chorion, discrepant methods of collecting embryos, and the paucity of toxicity data, implying the necessity to standardize G. rarus embryo tests and validate the sensitivity with various types of chemicals. This unique review allows us to conclude that G. rarus studies could be used in worldwide registrations and that further investigations are needed to use G. rarus embryos as alternatives to the fish test. Environ Toxicol Chem 2021;40:2680-2692. © 2021 SETAC.

Investigations on sediment toxicity of German rivers applying a standardized bioassay battery

River sediments may contain a huge variety of environmental contaminants and play a key role in the ecological status of aquatic ecosystems. Contaminants adsorbed to sediments and suspended solids may contribute directly or after remobilization to an adverse ecological and chemical status of surface water. In this subproject of the joint research project DanTox, acetonic Soxhlet extracts from three German river sediments from the River Rhine (Altrip and Ehrenbreitstein with moderate contamination) and River Elbe (Veringkanal Hamburg heavily contaminated) were prepared and redissolved in dimethyl sulfoxide (DMSO). These extracts were analyzed with a standard bioassay battery with organisms from different trophic levels (bacteria, algae, Daphnia, fish) as well as in the Ames test and the umuC test for bacterial mutagenicity and genotoxicity according to the respective OECD and ISO guidelines. In total, 0.01% (standard) up to 0.25% (only fish embryo test) of the DMSO sediment extract was dosed to the test systems resulting in maximum sediment equivalent concentrations (SEQ) of 2 up to 50 g l(-1). The sediment of Veringkanal near Hamburg harbor was significantly more toxic in most tests compared to the sediment extracts from Altrip and Ehrenbreitstein from the River Rhine. The most toxic effect found for Veringkanal was in the algae test with an ErC50 (72 h) of 0.00226 g l(-1) SEQ. Ehrenbreitstein and Altrip samples were about factor 1,000 less toxic. In the Daphnia, Lemna, and acute fish toxicity tests, no toxicity at all was found at 2 g l(-1) SEQ. corresponding to 0.01% DMSO. Only when increasing the DMSO concentration the fish embryo test showed a 22-fold higher toxicity for Veringkanal than for Ehrenbreitstein and Altrip samples, while the toxicity difference was less evident for the Daphnia test due to the overlaying solvent toxicity above 0.05% dimethyl sulfoxide (DMSO). The higher toxicities observed with the Veringkanal sample are supported by the PAH and PCB concentrations analyzed in the sediments. The sediment extracts of Altrip and Veringkanal were mutagenic in the Ames tester strain TA98 with metabolic activation (S9-mix). The findings allow a better ecotoxicological characterization of the sediments extensively analyzed in all subprojects of the DanTox project (e.g., Garcia-Kaeufer et al. Environ Sci Pollut Res. doi: 10.1007/s11356-014-3894-4 , 2014; Schiwy et al. Environ Sci Pollut Res. doi: 10.1007/s11356-014-3185-0 , 2014; Hollert and Keiter 2015). In the absence of agreed limit values for sediment extracts in standard tests, further data with unpolluted reference sediments are required for a quantitative risk assessment of the investigated polluted sediments.