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Toxicity Tests

A toxicity test determines if water is toxic using an animal called a Ceriodaphnia dubia, commonly referred to as a "water flea".

Ceriodaphnia dubia is a small crustacean found in vernal pools and in freshwater ponds and lakes throughout the world. Ceriodaphnia is very sensitive to pesticides, heavy metals, and other toxic substances used by humans discharged into surface waters as well as many naturally occurring substances and conditions. These properties make Ceriodaphnia a good organism for testing the toxicity of freshwater. Natural waters can become poisonous to the organisms that live in these waters when pollutants enter the water in too high a concentration. In a toxicity test, the Ceriodaphnia is placed in the water being tested and in an amount of clean water called the "control." If the organisms in the control live and the organisms in the test sample die, we know that they were initially healthy and something which is present in the sample (but not in the control) had caused their mortality. The water sample is considered "toxic." It does not, however, differentiate between naturally occurring g toxins or conditions, and man-made toxins or conditions.  Each water quality test is carried out using special instruments and water samples are taken from the river, storm drain, or street at each drain spot by the different teams. Each team will also observe physical changes around their sites.

Stephen Clark from Pacific EcoRisk instructed the Storm Drain Detectives on how to perform the tests with accuracy. A second training for the '01-'02 SDD was held in October '01.

Results for Toxicity


There had not been a storm event for over 200 days when sampling was done. The results show no toxicity; i.e. no statistical difference in survival to adult Ceriodaphnia dubia exposed for 48 hours under static conditions between the controls and the samples (see below).

Site 1: Cluff Avenue storm water pumping station – 100% survival

Site 2: Mokelumne River near Lodi Lake – 100% survival.

Site 3: Lagoon between Mokelumne River and Lodi Lake –  95% survival.

Site 4: Quail Lake in Stockton, CA –  100% survival.

Site 5: Mokelumne River n/of Lodi near Kennison Lane –  100% Survival.

Control: 100% survival

Control – low salt: 95% survival

Control – high salt: 0% survival


All five water samples taken from the Mokelumne River after a major storm event on 1/9/01 were found to be not toxic to adult Ceriodaphnia dubia exposed for 48 hours under static conditions


The first major storm event of the year was sampled after .30" rain had fallen. Eight water samples were collected from local sites including:

Site 1: Mills and Tienda Drive--storm drain runoff (new construction in area, storm drain berms in place, high leaf litter) 100% survival.

Site 2: South Lodi shopping center parking lot puddle--100% survival.

Site 3: West Lodi shopping center and urban runoff--100% survival.

Site 4: West Lodi shopping center wood roof PVC downspout runoff--100% survival.

Site 5: Mokelumne River, just below Lodi Lake--east of Woodbridge cemetery (end of storm drain system)--60% survival.

Site 6: Boat dock, Parson's Point, Lodi Lake--0% survival

Site 7: Urban containment pond.

Site 8: Control water + diazanon (400ng/L)--6.7% survival.


The references for information found on this page can be found in the Acknowledgements link, reference 5.




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