The State Water Resources Control Board (SWRCB) has released a report summarizing toxicity in California waters identified by the state’s Surface Water Ambient Monitoring Program (SWAMP) between 2001 and 2009. Unfortunately, the report does not include the widespread toxicity in non-SWAMP monitoring or toxicity identified pursuant to mandated monitoring by wastewater dischargers under their NPDES permit requirements.
Regardless, the report demonstrates widespread toxicity in surface waters. Toxicity was observed in the water column or sediment at 473 of the 992 sites where monitoring occurred. In other words, toxicity was found at 48% of the monitored sites.
In the Central Valley, 75% of the 298 sites were surface water was monitored were found to be toxic and sediment toxicity was found at more that 38% of the 212 sites where sediments were analyzed. In the San Francisco Bay area, 35.5% of the 48 surface water sites and 62.7% of 102 sediment sites were toxic. For the Central Coast, 56% of the 109 surface water sites and 34.9% of sediment sites were toxic.
Agriculturally dominated sites were found to be the most toxic (about 58% experienced toxicity) followed by urban sites (about 47%) and Ag-urban sites (47%). Toxicity was identified at only about 18% of undeveloped sites.
The report observes that the results may underestimate ambient toxicity because most samples were collected as “grabs” by filling a sample bottle or collecting sediment at one point in time. Toxic chemicals often flow downstream in pulses. Studies in which test organisms were caged in-stream often have detected toxicity when grab sample tests have not.
Toxicity tests also do not reveal the widespread sublethal impacts of chemicals and mixtures of chemicals in combination with other environmental stressors. Numerous studies in the scientific literature demonstrate adverse effects of chemical exposure well below water quality criterion. Nor do they address impacts of constituents that bioconcentrate and/or bioaccumulate in the tissue of aquatic organisms. It should also be noted that the toxicity tests did not always use the most sensitive species.