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Toxicity to aquatic algae and cyanobacteria

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Craigie and Hutzinger (1975) determined the toxicity of a C20-30, 50% wt Cl product to three species of marine algae (Dunaliella tertiolecta, Olisthodiscussp.and Thalassiosira fluviatilis). The tests were carried out for 6 days at 20°C. The chlorinated paraffin was dissolved in acetone and an appropriate volume of this solution was added to the flask and evaporated to dryness under a jet of air. Natural sea water (30 ml) was then added to the flasks and the flasks were stoppered with a cotton wool bung and autoclaved. The nominal chlorinated paraffin concentrations tested were 1 mg/l and 100 mg/l but no measurements were carried out to verify the actual exposure concentration. The test was started by adding a 1 ml inoculum of 3 to 4 day old algal culture to the flask and each flask was shaken by hand twice daily. Each concentration was tested in duplicate. The algal biomass was determined by turbidity measurements after 6 days exposure. No effects on biomass was seen in any of the exposed populations (the turbidity of the solutions was within 96‑105% of the control values.

 

The validity of this test is highly questionable as the method of administration of the test substance may not have been appropriate. It appears that an acetone solution of the substance was added directly to the test vessel and evaporated to dryness before the test water was added, and then the vessel was autoclaved (the temperature was not stated). As this substance is likely to be highly adsorptive onto the glass vessel used, and twice daily shaking of the vessel was the only method used to effect mixing, it is highly uncertain that all the chlorinated paraffin added would be in solution, or even in suspension and it is possible that most of it remained adsorbed onto the test vessel. As no monitoring was carried out during the test it is not possible to determine if any substance was lost during the autoclaving procedure (UK EA 2009).

 

For chlorinated paraffins as a whole, toxicity seems to decrease as chain length and degree of chlorination increase. Measured algal data are available for the homologues SCCPs and MCCPs, which are presented below. These data suggest that LCCPs would not be expected to exert effects on freshwater algae below their limit of water solubility. 

 

Predictions of algal toxicity have not been presented as the model used does not perform well for these kinds of substances.

 

SCCP Algal Toxicity

 

Several valid studies on freshwater and marine algae are available for SCCPs. 96-hour EC50s range from 0.043 to 3.7 mg/l, with the marine algaSkeletonemacostatumappearing to be more sensitive to short chain length paraffins than the freshwater algaSelenastrum capricornutum(96-hour EC50 = 3.7 mg/l based on cell density by particle count). 

 

It should be noted that the EC50 value given forSelenastrumexceeded the highest mean measured concentrations of the test substance; it is an extrapolated value. Further, the toxic effects seen with the marine alga were transient, with no effects being seen at any concentration after 7 days exposure.

 

MCCP Algal Toxicity

 

The toxicity of a C14‑17, 52% wt. Cl paraffin to the green algaSelenastrum capricornutumwas determined in a valid study using OECD method 201. Overall, very little effect on algal growth was observed in the test. The maximum inhibition in the growth rate seen was 3%, and the maximum inhibition of biomass was 18%. No clear dose‑response curve was determined. The NOEC from the test is around 0.1 mg/l (nominal), but it should be noted that no statistically significant effects were seen at some higher concentrations. The low levels of inhibition seen mean that it is not possible to derive an EC50from the test.