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Ref: ECP JJ901 T10 27 July 2001

Mr R Hadley
Biosystems SA
P O Box 53276
KENILWORTH
8000


Dear Mr Hadley

Enclosed are graphs and a table of results from toxicity tests performed on the oil dispersant sample which you submitted to us. Your effluent was tested in serial dilutions of seawater using gametes of the sea urchin Parechinus.

In these tests, urchin sperm is added to dilute effluent in seawater and allowed to swim for exactly 10 minutes. Newly spawned eggs are then added to each vial and fertilization is allowed to proceed for the following 10 minutes. After precisely 20 minutes formalin is added to each vial, to terminate the test.

A fertilised urchin egg forms an easily discernible hyaline membrane immediately upon being fertilized. Thus percentage fertilization can be assessed for each vial. Control vials, containing pure seawater, are used as checks and to supply data to compare with the vials containing effluent. By using serial dilutions (eg. 1:100, 1:200, 1:500, 1:1000) a series of points is obtained from each test, which can be presented in graph form. Each dilution is replicated four times, to improve the statistical value of the results.

From the variation in percentage fertilization within replicates and between dilutions, we calculate the variability of the test, and can calculate confidence limits within which all test results should fall if the effluent had no effect on the result. Results falling outside these limits would indicate a significantly reduced fertilization caused by the presence of toxicant in the water. The mean fertilization percentage of the controls in the test (see Table 1) adjusted down by 1 standard deviation (SD), yield a straight line across the top of the graph (see graphs 1-3). The mean % fertilization from each test dilution, plotted on the same graph, will typically yield a sigmoid curve. The point at which this curve intersects the straight line of the control results, when plotted down to the x-axis, will provide the Minimum Acceptable Toxicant Dilution (MATD). This is the minimum dilution in seawater at which the test fertilization was not significantly different from the controls of pure seawater.

The MATD of oil dispersant was 125 (Table 1), which is low, particularly considering that we were testing the concentrated product. In our experience of oil dispersant toxicity, this is a good result. Of course we cannot comment on the oil dispersion capabilities of the product, but if these are comparable with other oil dispersants then this product has an added advantage in terms of its low toxicity. In cases like this we have found it useful to test the product against other dispersants, in order to put the comparison into context, but generally we have found oil dispersants to have a toxicity one or two orders of magnitude higher than the MATD yielded by this dispersant.

If we can assist further with interpretation of the above please do not hesitate to call. We enclose an invoice for your attention. Thank you for using our toxicity testing facility.

Yours sincerely



Dr Allan Connell
Environmentek:CSIR:KwaZulu-Natal


Table 1