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Hard Science

A Reference Envelope

A hunt for some of the Bay's cleaner corners, as compared with its toxic hot spots, has yielded five good candidates to date. These candidate reference sites - whose sediments were run through 7-9 different toxicity tests both before and after last year's heavy rainfall and whose test results were then compared with results from 43 suspected toxic hot spots - showed consistently low contamination and toxicity to organisms, according to an S.F. Regional Board study still in progress.

The two-year study, a draft of which should materialize later this summer, aims to come up with better in-Bay reference sites and more realistic toxicity tests for use by Bay dredgers, dischargers, toxic cleanup planners and regulators. Part of the impetus for the study came in 1992, when tests at long-thought pristine reference sites in Tomales Bay and Bolinas Lagoon yielded wildly variable results (sediments proved toxic to 20-90% of test organisms). The variability raised questions about the suitability not only of the sites as a consistent reference for regional natural background conditions but also of the toxicity testing methods themselves. Hence the new research has focused on locating new reference sites, testing the sites and testing the tests.

The Board's Karen Taberski is still adding up all the numbers, but she says five good potential reference sites have emerged, and two of the nine possible toxicity testing methods are proving the most useful and consistent. The first method places the amphipods Eohaustorius or Ampelisca (shrimp-like aquatic organisms) in sediments for ten days and measures their survival. The second method places sea urchin larvae in porewater (water centrifuged from sediments) and assesses their development. Researchers also experimented with a variation in which they placed the urchins in a series of tubes that more realistically mimic conditions at the sediment/ water interface where many aquatic organisms live than the porewater test.

Comparing the two different exposures to the urchins, Taberski says they've found a good relationship - one test confirms the results of the other. The Board may decide to use the amphipod and sea urchin porewater tests for screening possible toxic hot spots and the urchin sediment/water interface test as a follow-up confirmation test.

By the time the study is finished, these new testing protocols and other details on how to use the reference sites will all become part of what Taberski calls a "reference envelope - a holistic way of evaluating what is toxic."

Contact: Karen Taberksi (510)286-1346

Science Curriculum gets an "A"

A recent statewide grading of environmental education materials gave Estuarine Encounters As and Bs. Citing this habitat-based, interdisciplinary curriculum guide's "incredible scope" and "excellent format," California's Department of Education recommended it for both primary and secondary students. The guide teaches students about current pollution, wetlands and other Bay-Delta environmental issues through the study of organisms that live in eight major estuarine habitats. This highly regarded teaching tool was developed by the S.F. Estuary Project's education program.

Contact: Steve Cochrane (510)286-0769

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