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Toxicity to aquatic algae and cyanobacteria

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In a GLP study conducted according to OECD Guideline 201, the 72-h NOEC, EC50 (0-72 h) for growth and EC50 (24-72 h) for growth rate for trisodium EDDS were 0.125, 0.29 and 1.57 mg/L for the green alga (Chlorella vulgaris) in freshwater (Neven and Henderix, 1990). For algae, the findings from this test are not considered as measures of direct toxicity, but an effect of overchelation of the essential metals in the growth media and resulting nutrient depletion (Schowanek et al. 1996).
In several, subsequent modified OECD Guideline 201 studies to GLP, the influence of varying medium concentrations of trace metals (cobalt, copper and zinc) with the use of natural river water, and in addition increasing levels of water hardness and use of media different from the OECD standard, were assessed in an attempt to understand their influence on the growth inhibition of EDDS acid. With increasing concentrations of trace metals, algal growth was increasingly less inhibited by EDDS acid at 1 mg/L (Hanstveit and Oldersma, 1993). The use of river water or increasing water hardness did not significantly influence the algae growth inhibition effects (Hanstveit and Oldersma, 1994a,b). In the presence of trisodium EDDS it was observed that addition of up to 1.2 mg/L to Medium 2M resulted in a similar or higher growth rate than in the controls (considered the NOEC in this study), and a EC50 of approximately 9.5 mg/L was derived. The effect pattern of trisodium EDDS and EDDS acid on algal growth can be best explained by trace metal toxicity and deficiency, due to complexation by the test substance (Hanstveit et al. 1994).
In a reliable study, [S,S]-EDDS acid, at concentrations of up to 100 mg/L, caused only minimal inhibition of photosynthesis (up to 14% after 8 min incubation) to the freshwater green alga, Selenastrum capricornutum. The EC50 was therefore greater than 100 mg/L (Schowanek et al. 1996).

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Additional information

Standard growth inhibition study (with trisodium EDDS):

In a GLP study conducted according to OECD Guideline 201, the effect of trisodium EDDS on the growth of a unicellular freshwater green algal species, Chlorella vulgaris, was assessed under semi static conditions. The test was carried out with an initial concentration of 1.2 x 104 cells/mL of C. vulgaris in the test cultures (in triplicate), for an exposure duration of 72 h. The nominal concentrations tested were 0, 0.032, 0.065, 0.125, 0.25, 0.50 and 1.0 mg/L for the determination of the concentration that caused 50% reduction (EC50; using the measured absorbances of the algal suspensions) in either growth or growth rate relative to the control culture. Under the conditions of this study, the 72-h NOEC, EC50 (0-72 h) for growth and EC50 (24-72 h) for growth rate of C. vulgaris were 0.125, 0.29 and 1.57 mg/L, respectively, following exposure to trisodium EDDS in freshwater (Neven and Henderix, 1990).

For algae, the findings from a standard OECD test are not considered as measures of direct toxicity, but an effect of overchelation of the essential metals in the growth media and resulting nutrient depletion (Schowanek et al. 1996). If algal laboratory data are extrapolated to the field in this way an unrealistically low PNEC value would be obtained (Jaworska et al. 1999). A number of more recent studies have been designed in an attempt to better understand the intrinsic toxic effects of trisodium EDDS on algae.

 

Effect of metal-enriched algal medium (with EDDS acid):

In a GLP study conducted according to a modified OECD Guideline 201 method, the relationship between the medium concentration of trace metals cobalt (Co), copper (Cu) and zinc (Zn) and the growth inhibition of EDDS acid to C. vulgaris, were determined. Addition of EDDS acid at 1 mg/L (only tested concentration) to OECD medium strongly inhibitted algal growth. However, with increasing concentrations of trace metals, algal growth was increasingly less inhibited by EDDS acid (Hanstveit and Oldersma, 1993).

 

River water spiked with OECD nutrients (with EDDS acid):

In a GLP study conducted according to a modified OECD Guideline 201 method, the addition of EDDS acid at a concentration of 1 mg/L (the only tested concentration) to natural river water medium for 96 h reduced the growth rate of C. vulgaris by 35% compared to controls (Hanstveit and Oldersma, 1994a).

 

Effect of water hardness (with EDDS acid):

In a GLP study conducted according to a modified OECD Guideline 201 method, addition of 1 mg/L of EDDS acid inhibited the growth rate of C. vulgaris by an average of 27% over 163.5 h, compared to controls. The lower growth rate, however, resulted in the same biomass yield as in the control but after a longer incubation period. It was observed that the water hardness level did not affect the inhibition of algal growth by EDDS acid (Hanstveit and Oldersma, 1994b).

 

Effect of metal-enriched algal medium (with trisodium EDDS):

In a GLP study conducted according to a modified OECD Guideline 201 method, the growth inhibition of trisodium EDDS to C. vulgaris, under semi-static conditions, in relation to the medium concentration of the trace metals Co, Cu and Zn was assessed. Trisodium EDDS concentrations of 0, 0.37, 0.75, 1.2, 2.5, 3.7, 6.1 and 12.3 mg/L were added to either the standard OECD medium (additional control) or a different media (Medium 2M) containing the trace metals Co, Cu and Zn at about 100, 850 and 145 times higher, respectively, than in the standard medium. One sample was taken from each flask after 0, 21.5, 48, 72.5, 92.5 and 143 h, and the number of cells and cell volumes assessed. The increased trace metal concentrations in Medium 2M resulted in a lower algal growth rate than compared with the standard OECD test medium. In the presence of trisodium EDDS it was observed that addition of up to 1.2 mg/L to Medium 2M resulted in a similar or higher growth rate than in the controls (considered the NOEC in this study), but reduced growth was seen at 2.5 mg/L and above (particularly after 72.5 h), and a EC50 of approximately 9.5 mg/L was derived. The EC50 with respect to inoculum viability was 1.8 mg/L. The effect pattern of trisodium EDDS on algal growth can be best explained by trace metal toxicity and deficiency, due to complexation by the test substance (Hanstveit et al. 1994).

 

Effect on inhibition of photosynthesis (with EDDS acid):

In a good-quality study, [S,S]-EDDS acid was tested for its ability to inhibit photosynthesis in the freshwater green alga, Selenastrum capricornutum. This method was used because the test substance is a chelating agent capable of binding metals essential for growth that are present in culture media; an effect that could confound the interpretation of a standard growth test. The algal cells were incubated in pH 7.5 buffer with levels of EDDS acid at up to 100 mg/L under a light source for 30 min to equilibrate before the addition of radiolabelled sodium bicarbonate solution as a source of CO2 for photosynthesis. Duplicate chambers were prepared for each test concentration. Samples were removed at 2, 4, 8 and 20 min and an equal volume of 2N hydrochloric acid was added to volatilise the remaining non-fixed carbon. The cells were then dried and the carbon uptake determined by liquid scintillation counting. At 100 mg/L, the test substance caused a minimal reduction in 14CO2 fixation rate of about 10% after 4 min and 14% after 8 min; the fixation rate was linear up to about 8 min, after which the supply of 14CO2 became limiting. All other concentrations produced no reduction, or actually stimulated photosynthesis. The positive control (copper) induced a 50% inhibition of photosynthesis at 0.1 mg/L. The EC50 for photosynthesis was greater than 100 mg/L when [S,S]-EDDS acid was incubated with S. capricornutum in an algal short-term photosynthesis inhibition test (Schowanek et al. 1996).

 

This test assesses the interaction of the test substance with the photosynthesis process, an endpoint integrating various cellular processes, and a possible alternative endpoint to growth (Peterson and Nyholm, 1993). The short timescale of the test allows the algae to survive on stored nutrients, thus eliminating any effects due to nutrient availability. The test has been shown to be less sensitive than, but to correlate well overall with, longer growth tests (Versteeg, 1990).

[Data on trisodium EDDS is considered relevant to use for understanding the potential effects of EDDS acid on algal growth, and is acceptable for using as read-across information.]

 

No data on marine algae or cyanobacteria are currently available for EDDS acid or its simple salts.

 

References (not included elsewhere in IUCLID dossier - need to move to reference list in CSR)

Jaworska JS et al. (1999). Environmental risk assessment for trisodium [S,S]-ethylene diamine disuccinate, a biodegradable chelator used in detergent applications. Chemosphere 38, 3597-3625.

Peterson HG and Nyholm N (1993). Algal Bioassays for Metal Toxicity Identification. Water Pollution Research, Journal of Canada 28, 129-153.

Versteeg DJ (1990). Comparison of short and long-term toxicity test results for the green alga, Selenastrum capricornutum. In: "Plants for Toxicity Assessment", ASTM STP 1091. Wang W, JW Gorsuch and WR Lower (eds). American Society for Testing and Materials, Philadelphia pp. 40-48.