Arsenic acid

Toxicity to aquatic algae and cyanobacteria

Description of key information

In a 14-days toxicity study, the cultures ofAnkistrodesmus falcatuswere exposed to Disodium arsenate (Na2HAsO4.7H2O) at nominal concentrations of 0, 0.01, 0.10, 1.0, 10, 25, 50, 75 and 100 mg/L (based on As(V)) under static conditions in accordance with the Algal Assay Procedure Bottle Test (US EPA 1971) and APHA (1975) test methods. The parameter followed is growth based on Chlorophyll a measurement compared to control. The 14d-EC50 is determined to 0.256 mg/L based on nominal concentrations of As(V). The corresponding NOEC was 0.01 mg/L. Even if the test method used is obsolete, the study design and the results are well documented. This toxicity study is classified as reliable with restrictions for algae toxicity study.

Key value for chemical safety assessment

EC50 for freshwater algae:

0.159 mg/L

EC10 or NOEC for freshwater algae:

0.01 mg/L

Additional information

A large data set is available on the toxicity of Arsenic acid to algae and aquatic plants.

 

Long term toxicity data

In the study of Vocke, 1980, several algae species were tested and resulted in 14d EC 50 of 0.048 mg/L to 30.7 mg/L. In the study of Conwell, 1978, the resulting 24 days NOEC was 60 µg/L. This indicates that there is a large variability of sensibility between the species. The lowest result was a NOEC of 0.01 mg/L observed in a 14 d toxicity study onAnkistrodesmus falcatus.

Moreover, there are several references available on algae toxicity data that are either not detailed enough or that do not result in NOEC or EC50 type results.

In a 14-days toxicity study, the cultures ofAnkistrodesmus falcatuswere exposed to Disodium arsenate (Na2HAsO4.7H2O) at nominal concentrations of 0, 0.01, 0.10, 1.0, 10, 25, 50, 75 and 100 mg/L (based on As(V)) under static conditions in accordance with the Algal Assay Procedure Bottle Test (US EPA 1971) and APHA (1975) test methods. The parameter followed is growth based on Chlorophyll a measurement compared to control. The 14d-EC50 is determined to 0.256 mg/L based on nominal concentrations of As(V). The corresponding NOEC was 0.01 mg/L. Even if the test method used is obsolete, the study design and the results are well documented. This toxicity study is classified as reliable with restrictions for algae toxicity study.

In a 14-days toxicity study, the cultures ofScenedesmus obliquuswere exposed to Disodium arsenate (Na2HAsO4.7H2O) at nominal concentrations of 0, 0.01, 0.10, 1.0, 10, 25, 50, 75 and 100 mg/L (based on As(V)) under static conditions in accordance with the Algal Assay Procedure Bottle Test (US EPA 1971) and APHA (1975) test methods. The parameter followed is growth based on Chlorophyll a measurement compared to control. The 14d-EC50 is determined to 0.048 mg/L based on nominal concentrations of As(V). Even if the test method used is obsolete, the study design and the results are well documented. This toxicity study is classified as reliable with restrictions for algae toxicity study.

In a 14-days toxicity study, the cultures ofSelenastrum capricornatumwere exposed to Disodium arsenate (Na2HAsO4.7H2O) at nominal concentrations of 0, 0.01, 0.10, 1.0, 10, 25, 50, 75 and 100 mg/L (based on As(V)) under static conditions in accordance with the Algal Assay Procedure Bottle Test (US EPA 1971) and APHA (1975) test methods. The 14d-EC50 value is based on growth based on Chlorophyll a measurement. The 14d-EC50 is determined to 30.761 mg/L based on nominal concentrations of As(V). Even if the test method used is obsolete, the study design and the results are well documented. This toxicity study is classified as reliable with restrictions for algae toxicity study.

Another validated reference is the study of Conwell,a 24-days toxicity study, the cultures ofAsterionellawere exposed to arsenate at nominal concentrations of8, 60 and 160 µg/L (as As)under flow through conditions. The 24d-EC50 value is based on growth and oligo elements use. The 14d-EC50 is determined to 30.761 mg/L based on nominal concentrations of As(V).Even if the test method used is obsolete, the study design and the results are well documented. This toxicity study is classified as reliable with restrictions for algae toxicity study.

 

Acute toxicity data

From the document “Proposed EQS for Water Framework Directive Annex VIII substances: arsenic (total dissolved)”, the most severe reference for acute toxicity on algae is the study of Chen, 1994, is a EC50 of 0.159 mg/L of As as arsenicpentoxidetoScenedesmus obliquus.The study was conducted in semi-static conditions, the concentrations used were: 0, 50, 100, 200, 300μg l^-1. The study lasted 96h hours. There are few details missing for methodology, but since the study is based on semi-static regime it is considered as valid.