Sodium azide

Endpoint summary

Description of key information

Data describing the acute aquatic toxicity of sodium azide to aquatic organisms are available for fish, invertebrates, algae and microorganisms.

Fish:

The available data on short-term toxicity to fish show LC50(96h) values in the range 0.7-5.5 mg/L. Also LC100 values are reported which are in the range of 3.0 mg/L (96h) and 10 mg/L (24h). The latter values can be regarded as derived from a limit test, since no other concentration was tested. The 96 h LC50 from the key study (Klaverkamp et al. 1975) is 2.75 mg/L for Oncorhynchus mykiss.

 

Aquatic invertebrates:

Reported LC50(48h) values for aquatic freshwater invertebrates are in a similar concentration range (0.4-6.4 mg/L). Effect values from a handbook (Klimisch 2) indicate 48 h EC50 values for Daphnia pulex (4.2 mg/L), Simoceephalus sp. (6.4 mg/L) and Gammarus fasciatus (5.0 mg/L) in a similar range. Studies conducted with Paracentrotus lividus, Orconectes rusticus and Procambarus clarkii report lower effect concentrations: In a study by Bills et al. (1988) a LC100 (96h) of 1.0 mg/L (Orconectes rusticus) was derived; the outcome of this is a LC50 of <1.0 mg/L. This is in accordance with the results from Hughes 1966 who derived for Procambarus clarki the following effect concentrations:

LC0 (48 h) = 0.4 mg/L

LC100 (48 h) = 0.6 mg/L

LC0 (96 h) = 0.4 mg/L (autotomy, observed)

LC100 (96 h) = 0.6 mg/L

Bills et al (1988) and Hughes et al. (1966) are rated with Klimisch 3 and 4 due to unsuitable test system and missing documentation. Nevertheless the two independent studies present evidence that the EC50 value for Sodium azide towards aquatic invertebrates might be below 1 mg/L and above 0.4 mg/L.

Concerning marine species one study is available which was conducted similar to EPA/600/R-95-136 (Short-term methods for estimating the chronic toxicity of effluents and receiving waters to west coast marine and estuarine organisms). They exposed the marine species Holmesimysis costata to Sodium azide and derived a LC50 (7 d) of 149 µg/L and a NOEC (7 d) of 100 µg/L. As the test lasted 4 days longer than the standard acute toxicity test for invertebrates (i.e. 48 h) it is reasonable that the LC50 is lower than for the organisms exposed for only 48 h. Nevertheless this value should be used for estimating the marine PNEC.

 

Algae:

For algal toxicity, the well conducted work of Hickey et al. (1991) is regarded as key study, reporting an EC50 (96h) of 0.35 mg/L. Two other studies on algal toxicity were found, reporting LC50 (24h) = 176 mg/L (Krebs 1991) and EC50(48h) = 70.7 mg/L (Hunt et al. 1996). These values are substantially higher than the one in the key study, however, all two studies show methodological deficiencies (e.g. markers of algal growth, selection of test concentrations) which disqualify them as key study.

Comparing the results from the three trophic levels, algae appear to be the most sensitive. Therefore, the EC50 (96h) of 0.35 mg/L is used to derive a PNEC freshwater.

 

Classification & Labelling:

Taken together, several studies in all three trophic levels show LC/EC50 values of <1 mg/L. Furthermore, as no data on biodegradability in water are available, Sodium azide must be regarded as not rapidly degradable. These two facts force a categorization according to OECD GHS into Category Chronic I. Labelling requires the signal word “Warning” and the hazard statement “Very toxic to aquatic life with long-lasting effects”.