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Short-term toxicity to aquatic invertebrates

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Description of key information

The lowest valid value for acute toxicity to a standard invertebrate species for classification purposes is 12.2 mg Sb/L for Daphnia magna (Kimball, 1978).

The lowest reliable value for acute toxicity to freshwater invertebrates is 1.77 mg Sb/L for Chlorohydra viridissimus (TAI, 1990).

No valid acute studies with marine invertebrates were identified for antimony.

Key value for chemical safety assessment

Additional information

Four reliable studies on the acute toxicity of antimony to freshwater invertebrates have been identified: Kimball (1978), Yang (2014), TAI (1990) and Brooke et al. (1986). There is also an additional study by Brooke et al. (1986) which, although not considered reliable, does support the finding of TAI (1990) that the coelenterate hydra is the most sensitive invertebrate tested to date.

In the study by Kimball (1978), neonates of the cladoceran Daphnia magna (<1 d old) were exposed for 2 or 4 days to antimony (added as SbCl3) in a static test design. This study was performed with six concentrations (range: 1.65 – 44.15 mg Sb/L) and a control, using four replicates with ten neonates for each concentration. Mortality was the endpoint. In the 2-day exposure regime, the daphnids were exposed to antimony (SbCl3) either with or without feeding. The resulting LC50values were 12.2 and 18.8 mg Sb/L, respectively. The outcome of the 4-day exposure (LC50 of 12.1 mg Sb/L) was not considered for assessing acute antimony toxicity because the test design was not in line with OECD-recommendations as outlined in OECD Guideline No.202 (test duration, administration of food during the exposure period).

Doe et al.(1987) also reported on the acute toxicity of Daphnia magna, but this study – although based on measured exposure concentrations – is considered unreliable as no information is presented on (i) the number of concentrations and which concentrations were used, (ii) dose-response curves (no raw data are available), (iii) the number of replicates (if any), and (iv) what statistics have been used to calculate the LC50 values.

Yang (2014) reported on the toxicity of antimony (as SbCl3) to the freshwater swamp shrimp Macrobrachium nipponense. No official guideline was followed, but reported methodology was in line with standard OECD-protocols for testing invertebrates . Test species originated from local commercial suppliers and were acclimated for two weeks to laboratory conditions prior to testing. (control + 8 test concentrations (0.5 – 16 mg Sb/L), two replicates/concentration, 10 organisms/replicate). Physicochemical conditions in the acclimation medium was similar to the conditions in the test media (pH 7.4-8.1 ; 7.0-7.7 mg O2/L ; hardness of 38 -45 mg/L as CaCO3; temperature of 24 +/- 0.5 °C : 12/12h L:D cycle). The 96h-LC50 was 1.96 mg Sb/L. It should be noted, however, that no indication is given whether this value is based on nominal or measured Sb-concentrations.

In the study by TAI (1990),), the acute toxicity of antimony (added as SbCl3) was determined fortwo hydra species (Hydra oligogactis, and Chlorohydra viridissima), one snail (Physa heterostropha), one midge (Chironomus tentans) and an amphipod (Hyalella azteca) in a static test design. The exposure period was four days. All tests were performed with five concentrations and a control, using duplicate replicates with five individuals for each test chamber. The measured concentrations used (nominal concentration within brackets) were 8.5 (15.6), 15.4 (31.25), 19.8 (62.6), 24.6 (125), and 21.22 (250) mg Sb/L, and a control with 0 mg Sb/L (measured concentration) for Physa heterostropha, Chironomus tentans, and Hyalella azteca. The measured concentrations used (nominal concentration within brackets) for the two hydra species Hydra oligogactis and Chlorohydra viridissima were 1.18 (0.5), 1.52 (1.0), 2.56 (2.5), 4.48 (5.0), and 5.42 (6.25), and a control with 0 mg Sb/L (measured concentration). These acute tests resulted in LC50s of 1.95, 1.77, 14.2, 4.1, and 21.6 mg Sb/L for Hydra oligogactis, Chlorohydra viridissima, Physa heterostropha and Chironomus tentans, respectively. Both Hydra species were found to be the most sensitive invertebrates that were assessed in this study.

This observation was further confirmed by Brooke et al. (1986) who also observed that hydra were be the most sensitive of several tested invertebrates (Hydra sp.,amphipods (Gammarus pseudolimnaeus), annelids (Lumbriculus variegatus), and caddisflies (Pycnopsyche sp.)).Adult hydroids (Hydra sp.) were exposed in a static test design to antimony (added as SbCl3) for 4 days. The evaluated endpoint, however, was tentacles clubbed and/or shortened body column and tentacles. Tests were performed in quadruplicate with five concentrations (range: 0.3 - 3.3 mg Sb/L) and a control, with each replicate consisting of ten hydroids.The resulting 24h-EC50 was 2 mg Sb/L (95%CL: 1.8 - 2.2 mg Sb/L), the 48h-EC50 was 1.0 mg Sb/L (confidence limits not reliable, according to authors), and the 96h-EC50 was 0.5 mg Sb/L (95%CL: 0.5 - 0.6 mg Sb/L). The results of both Hydra-studies cannot be compared as different endpoints were assessed: the TAI (1990) study considered the beginning of the break-down of tissue integrity and an associated bacterial growth enveloping the animals, while Brooke et al. (1986) used clubbed tentacles and/or shortened body column and tentacles as endpoint.

Tests on G.pseudolimnaeus, L.variegatus and Pycnopsyche sp.were performed in duplicate with only two concentrations (11.4 ± 3.9 and 25.7 ± 2.2 mg Sb/L) and a control, with each replicate consisting of ten individuals.Due to the limited number of test concentrations, the determination of a reliable EC50was not possible for these three species. However, as the observed effects in the highest test concentration were below 50%, the authors reported a “greater than > 25.7 mg Sb/L" value for these three species.The result of the hydra study can only be considere indicative, since the endpoint used (tentacles clubbed and/or shortened body column and tentacles) is subjective, and no additional information on the dose-response relationship is provided.

Borgmann et al. (2005) reported a seven-day acute LC50 value of 0.687 mg Sb/L for the amphipod Hyalella azteca. The objective of the study (large-scale screening of metal toxicity for categorization of substances on the Canadian Domestic Substances List) required some modifications to the standard experimental design. The main reason for invalidating this study is that antimony was clearly not the only toxicity-inducing factor in the test medium. This study used metal standards for toxicity testing. For antimony, a metal standard containing 20% HCl was used. The acid in the metal standards was neutralized by adding a solution of 1M NaHCO3 and 1M KOH in a 19:1 ratio. Along with a control treatment (containing normal test medium), an acid control was used (containing acid and neutralizing solution additions equal to the amount added in the tests with acidified metal standards). For metal standards supplied in 20% HCl, survival in the acid controls for the 1,000 µg/L treatment dropped to 32%, indicating that the organisms were adversely affected by the blank test medium. Therefore, toxicity in the metal treatments was most likely overestimated in this study, and reported LC50 values can therefore not be considered reliable. It should be noted that toxicity tests were also conducted using sodium antimonate (NaSbO3) as test substance. No toxicity was observed at the highest exposure concentrations tested (1 mg Sb/L nominal, 0.197 mg Sb/L measured).

Nam et al (2009) investigated the acute toxicity antimony potassium tartrate to the invertebrates M.macrocopa and S.mixtus. The generated LC50 values of 8.95 mg/L (48h) and 4.92 mg/L (24h), respectively, cannot be considered reliable for the hazard assessment of antimony and antimony compounds. The tests were performed according to OECD-guidelines, but the used test substance is deemed unsuitable: dissolved antimony forms a complex with tartrate, and therefore only a part of the total amount of antimony will be present as “free” antimony; the exact concentration of free antimony can only be estimated via speciation modeling. The reported LC50 values therefore represent the toxicity of the dissolved Sb-tartrate complex at equilibrium, and not the toxicity of the Sb-ion.

Fjallborg and Dave (2004) spiked sewage sludge with SbCl5 on which radish, oats or lettuce was grown after a 60-day equilibrium period. After a 14-day cultivation period; the toxicity of the elutriate to Daphnia magna was tested. The authors reported an EC50 based on the nominal spiked concentrations. The EC50’s of the elutriate after radish and oat cultivation were 22 mg Sb/kg and 5 mg Sb/kg, respectively. However, when the effects data are compared with the measured concentrations in the elutriate, no dose reponse is observed. For this reason, this non-standard study is not considered reliable for assessing acute antimony toxicity in the aquatic environment.

Overall, no reliable acute invertebrate studies with pentavalent antimony have been identified. There is therefore no information on the toxicity of exposures which contain a very high proportion of Sb(V), as only relatively limited oxidation of Sb(III) to Sb(V) would be expected within the time frame of acute toxicity tests that are conducted with a trivalent antimony substance. In oxygenated waters, Sb(V) is expected to be the dominant species although the rate of oxidation of Sb(III) to Sb(V) is very slow, with a half-life in laboratory solutions expected to be in the order of months (CanMET, 2010).

 

It should be noted that USEPA (1988) included results from Spehar (1987) of a study with the cladoceran Ceriodaphnia dubia that reported acute toxicity levels based on measured exposure concentrations. So far, the original study could not be acquired.

 

Conclusion:

The most sensitive of the aquatic invertebrates is the hydra, and the lowest valid 96h-EC50 for acute toxicity is 1.77 mg Sb/L. This value can be considered for PNEC-derivation if no chronic data would be available.

For hazard classification purposes, however, the lowest acute value for a reference standard species is the 48h-EC50of 12.1 mg Sb/L for Daphnia magna (Kimball, 1978). Indeed, the aim of a hazard assessment (i.e. classification), is not to protect all species from potential adverse effects; the classification tries to place every substance in pre-defined hazard categories (for various physicochemical, human health and environmental endpoints), and all substances within a specific category are expected to share a similar (eco)toxicological or physicochemical hazard profile. A ‘common’ hazard profile within a category, however, can only be achieved when substances are evaluated against the same benchmarks. The environmental classification should therefore only be based on relevant toxicity data that are generated from the recommended standardized testing procedures, using specified standard test species that represent either algae, invertebrates (crustaceans) or fish. Any deviation from these principles (use of other species/taxonomic group, exposure period or testing guideline) would compromise the basic principle that all substances within the same hazard category share a common hazard profile.

The CLP-Regulation provides specific guidance on the aquatic environmental acute toxicity data that can be used for the hazard assessment. According to the general definition of ‘acute aquatic toxicity’ given in the regulatory criteria (CLP Regulation EU 1272/2008, Section 4.1.2.7.1 ) (EC Regulation, 2008; 2011) and ECHA CLP guidance (ECHA 2015, version 4.1) a fish 96h-LC50 (OECD 203 or equivalent), a crustacea species 48h-EC50 (OECD 202 or equivalent), and/or an algal species 72h- or 96h- EC50 (OECD 201 or equivalent), determine the acute toxicity classification. These species are considered as surrogate for all aquatic organisms. Data on other species may also be considered, but only if the test methodology is suitable and equivalent to OECD Guidelines. The standard species/endpoints for invertebrates is the 48 hours Invertebrates/Crustacea first instar juveniles L(E)C50 mortality or immobilization (e.g. D. magna)

The Hydra-study does not meet several criteria of the OECD 202 guideline, most importantly the test duration, life stage and endpoint that were evaluated.