4-(2-chlorophenyl)-N-cyclohexyl-N-ethyl-5-oxo-4,5-dihydro-1H-tetrazole-1-carboxamide

Endpoint summary

Description of key information

Fish: LC50 (96 h) = 1.3 mg/L (nominal, similar to OECD 203, Plecoglossus altivelis)

Aquatic invertebrates: EC50 (48 h) = 0.1 mg/L (nominal, similar to OECD 202, Daphnia magna)

Algae: ErC50 (72 h) = 6.04 µg/L, NOEC (72 h) = 0.49 µg/L (initial measured, OECD 201, Pseudokirchneriella subcapitata)

Activated sludge microorganisms: NOEC (0.5 h) = 10000 mg/L (nominal, similar to OECD 209, activated sludge)

Additional information

Numerous experimental studies are available for all trophic levels investigating the short-term effects on various species of fish, different aquatic invertebrates, algae, and microorganisms. The chronic toxicity of the substance was investigated for algae only.

Six experimental studies are available testing the acute toxicity of the test substance towards fish. Five studies were conducted with five different species under freshwater conditions, i.e. Plecoglossus altivelis (Ayu fish; amphidromous species, moving between coastal marine waters and freshwater lakes and rivers), Oncorhynchus mykiss (reported as Salmo gairdneri irideus), Mugil cephalus (Gray mullet; an euryhaline species, which has the capability to acclimate to different levels of salinity and naturally occurs in coastal waters and freshwater rivers), and Cyprinus carpio (Common carp). A further study was conducted with the marine species Chrysophrys major (Red seabream).

None of the studies was conducted according to GLP. Three studies (1996a, 1996b, and 1996c) followed Japanese guidelines, dating to 1965 which was not further specified but comparable to the OECD guideline 203. All studies were conducted under static test conditions without replacement of test medium and either acetone or DMSO was used as a solvent. Test concentrations were not analytically monitored. Two reports (1993a, 1993b) provide only short summaries.

All determined LC50 values are in the same level of magnitude and range between 1.3 to 4.0 mg/L. Thus, these studies are considered to be used in a weight-of-evidence approach even though they were not conducted according to today’s standard methods. The lowest determined LC50 value of 1.3 mg/L was derived in the test with Plecoglossus altivelis (1994).

Three experimental studies are available testing the acute toxicity of the substance towards aquatic invertebrates. Test organisms used were water fleas (Daphnia magna) (1994b), clams (Corbicula japonica) (1996d), and shrimps (Paratya compressa improvisa) (1994c). None of the studies was conducted according to GLP. The study with Daphnia magna was conducted equivalent to OECD guideline 202, the study with clams followed Japanese guidelines dating to 1965 which was not further specified. No guideline is available for the test with shrimps.

All studies were conducted under static test conditions without replacement of test medium and either acetone or DMSO was used as a solvent. Test concentrations were not analytically monitored.

All results are used in the frame of a weight-of-evidence approach. The most sensitive value (EC50 (48 h) = 0.1 mg/L) derived by the experimental study with Daphnia magna was used as key value for this trophic level.

The studies investigating the toxicity to fish and aquatic invertebrates listed above do not fulfill nowadays guideline testing requirements and none of them can be considered as key study. However, in sum all of them provide basic data sufficient for hazard assessment purposes and therefore a weight-of-evidence (WoE) approach is followed here.

This approach is further justified by the fact, that aquatic algae (see below) demonstrated to be by far the most sensitive organisms, resulting in the most stringent classification of aquatic acute 1 and aquatic chronic 1, and that results with organisms from this trophic level furthermore are used for deriving PNECs and conducting the risk assessment.

Two experimental studies are available giving evidence on the toxicity of the substance towards algae. The first study with Pseudokirchneriella subcapitata as the test organism was performed according to the OECD guideline 201 and GLP standards (1997). A follow up study (1998) under GLP conditions investigated the recovery (in terms of growth rate and doubling times) of the algae Pseudokirchneriella subcapitata after exposure to the test item. The study was performed based on the principles of the OECD guideline 201 as well. Analytical monitoring was conducted. The effect values of 6.04 µg/L and 0.49 µg/L determined in the study 1997c represent the key values for acute (ErC50) and chronic toxicity (NOErC), respectively. These values are the most sensitive effect values found for all aquatic organisms and are thus used for classification and risk assessment purposes.

According to Regulation (EC) No 1907/2006, Annex IX, Column 2, 9.1.6, long-term toxicity testing shall be proposed by the registrant if the chemical safety assessment according to Annex I indicates the need to investigate further the effects on aquatic organisms. In acute aquatic toxicity tests algae (ErC50 (72 h) = 6.04 µg/L, NOErC (72 h) = 0.49 µg/L, initial measured) was found being by far the most sensitive organisms, resulting in T (toxic) for PBT assessment. The difference between sensitivity demonstrated in fish (LC50 (96 h) = 1300 µg/L, nominal) compared to algae is factor 215. The difference between sensitivity between algae and aquatic invertebrates (EC50 (48 h) = 100 µg/L, nominal) is around factor 16. Therefore, it is neither to be expected that an additional chronic fish or aquatic invertebrates study will yield even lower effect values compared to algae nor will it contribute to a more stricter toxicity (T) assessment. The substance is classified as Aquatic Chronic 1 (H410) and Aquatic Acute 1 (H400) according to the consolidated version of Regulation (EC) No 1272/2008 and further amendments (ATPs) which is the highest aquatic toxicity classification.

In addition, the environmental exposure assessment for the test substance according to Annex XI, Section 3 of Regulation (EC) No 1907/2006 indicates no risk for the aquatic compartment (all RCR < 1; please refer to Chapter 9 and 10 of the Chemical Safety Report for detailed information). Therefore, chronic tests with fish and aquatic invertebrates are not deemed necessary. Especially, the substance is a herbicide which implicated plants to be the most sensitive organism group with the highest expected toxicity. Thus, no higher toxicity is expected for fish and aquatic invertebrates than for algae and no chronic test is proposed for fish and aquatic invertebrates.