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Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

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Link to relevant study record(s)

Description of key information

Algal inhibition: 8-day NOEC 425 mg/L (estimated from a Toxicity Threshold value of 640 mg/L, nominal) (equivalent to OECD 201), for the effects on S. quadricauda (Bringmann and Kuhn 1980), rel. 2.

It is noted that the measurement of toxicity of a complexing substance such as citric acid to aquatic algae and cyanobacteria is technically challenging as the substance can complex essential nutrients present in the test media so that they are not available to the test organisms.

Key value for chemical safety assessment

EC10 or NOEC for freshwater algae:
425 mg/L

Additional information

Bringmann and Kuhn (1980): An 8day Toxicity Threshold value of 640 mg/L and a NOEC value of 425 mg/L (estimated by reviewer) have been determined for the effects of citric acid on cell density of the algae Scenedesmus quadricauda. The pH was neutralised and there is sufficient information to assess the study, which has therefore been assigned reliability 2 and is considered to be key. Whilst it has been established that 8-day studies may not give a true estimation of toxicity due to the exponential growth of algae reaching a plateau, it is thought that the data in the supporting studies support the findings in Bringmann and Kuhn (1980).

Ohgai et al. (1993): Optimal growth recorded with the addition of 100 mg/L of citric acid with Tetraselmis tetrathele and with the addition of 30 mg citric acid/l to the medium with Chaetoceros gracilis, Navicula ramosissima, Pavlova lutheri. It should be noted that, based on the graphs presented in the paper, at 100 mg/L the cell densities of Chaetoceros gracilis, Navicula ramosissima, Pavlova lutheri appear to be comparable to that of the controls. At 300 mg/L the pH dropped to 3.8, therefore at this concentration and at 1000 mg/L negative effects due to low pH are likely. This is a publication in Japanese and only the abstract, tables and figures in the paper were available for review in English.

Bringmann and Kuhn (1978): An 8-day Toxicity Threshold (equivalent to a LOEC) value of >80 mg/L has been determined for the effects of the test substance on the growth rate of the algae M. aeruginosa. It is not clear from the paper whether pH was adjusted or not, therefore it has been assigned reliability 4.

In addition, the measurement of toxicity of a complexing substance such as citric acid to aquatic algae and cyanobacteria is technically challenging as the substance can complex essential nutrients present in the test media so that they are not available to the test organisms. This could result in apparent toxicity that is due to nutrient deficiency rather than true chemical toxicity. The above data has been generated without taking into account these properties, however, they indicate low toxicity of citric acid to algal organisms

A SafePharm 2006 study is reported in the CLH consultation on citric acid, indicating a 72 h EC50 2 mg/L and a NOEC 1.4 mg/L, both based on growth rate. A marked decline is test substance concentration over the course of the test was observed at all concentrations except 100 mg/l and these results are a conservative interpretation based on mean measured concentrations; an ErC50 of 26 mg/l and a 72 h NOEC of 12.5 mg/l were obtained based on nominal concentrations. A concentration dependent decrease in the pH with test substance concentration was observed. The study has been discounted on the basis that pH related effects are likely to have taken place. In addition, the dose-response curve is irregular, which is likely to be due to the complexation effects of citric acid. Access to the report has not been purchased, for details please refer to the CLH consultation here https://echa.europa.eu/documents/10162/c721decb-298f-92a3-b425-55cbf9c6cc9b [accessed January 2019].