A statewide investigation of urban creek sediment toxicity was conducted in California in recognition of increased incidences of toxicity linked to pyrethroid pesticides. The goals were to examine the spatial occurrence and magnitude of sediment toxicity in California urban creeks, and to examine the role of pyrethroids in toxic urban creek sediment samples. After a preliminary screening of 90 sites, 30 creeks were sampled in eight geographical regions. Sediment toxicity was assessed using 10 day bioassays with the resident amphipod Hyalella azteca. Bioassays were conducted at two test temperatures of 23 degrees C and at 15 degrees C to provide evidence of the cause of toxicity, and to more accurately reflect ambient environmental temperatures. Twenty-five of 30 samples were toxic when tested at 23 degrees C, and all 30 samples were toxic when tested at 15 degrees C. The magnitude of toxicity increased in samples tested at 15 degrees C suggesting the influence of pyrethroids, which are more toxic at colder temperatures. Pyrethroids were present in all sediment samples and were the only compounds detected at concentrations toxic to H. azteca. Bifenthrin was the pyrethroid of greatest toxicological concern, occurring in all 30 samples at concentrations up to 219 ng/g. Pyrethroid contamination of urban creeks was most severe in the Los Angeles, Central Valley, and San Diego regions, respectively. However, pyrethroids were also linked to urban creek aquatic toxicity in all regions sampled, including the less urbanized areas of the North Coast and Lake Tahoe.

Abstract-In recent years, populations of resident aquatic species in California's Sacramento-San Joaquin Delta, USA, have declined appreciably in numbers. The cause of these declines is not known, but has been attributed to a number of factors including water diversions, loss of habitat, introduced exotic organisms, and toxic compounds. To detect and characterize the spatial extent, severity, frequency, and causes of potential toxicity caused by anthropogenic pollutants, a monitoring study was conducted over a period of two years (1993)(1994)(1995). Sites were monitored on a monthly basis using the standardized U.S. Environmental Protection Agency freshwater toxicity test with the zooplankton species Ceriodaphnia dubia. Twenty-four sites were sampled in 1993 to 1994. During the 1994 to 1995 sampling season, the number of sampling sites was restricted to 20, with special emphasis placed on back sloughs, delta island agricultural drains, and main-stem river sites. Significant mortality or reproductive toxicity in C. dubia was detected in 9.8% of 400 water samples tested. Ecologically important back sloughs had the largest percentage of toxic samples. Of 71 and 103 samples collected from back sloughs during 1993 to 1994 and 1994 to 1995, respectively, 14.1% and 19.6% were toxic. To determine the causative chemical(s), toxicity identification evaluations (TIEs) were conducted on 23 toxic samples. These included eight follow-up samples taken to determine whether toxicity at the respective site persisted. Organophosphate (chlorpyrifos, diazinon, malathion) and carbamate (carbofuran, carbaryl) pesticides were identified as primary toxicants. Chlorpyrifos was present at toxic concentrations in 87% of samples tested by TIE. Analysis of data from the follow-up samples suggested that toxicity may have persisted over periods of several days to weeks.

The mucous trails secreted by certain species of intertidal limpets serve as adhesive traps for the microalgae that are their primary food resources. The mucous trails of two solitary homing limpets, Lottia gigantea and Collisella scabra, also stimulate the growth of microalgae. In contrast, the mucous trails of an aggregating limpet, Collisella digitalis, and the carnivorous dog whelk, Nucella emarginata, do not stimulate microalgal growth. These results may be explained by differences in the behavior of these gastropod species. Homing species can capitalize on the production of a food enhancing mucus because they have restricted home ranges and retrace their own mucous trails. The persistence time of mucus in the field varied with gastropod species, mucus type (i.e., mucus produced by moving or stationary limpets), and tidal height. Field studies suggest mucous trails can, but may not always, persist long enough to allow algal enhancement. Biochemical analyses suggest that the ability of mucous trails to trap microalgae adhesively is correlated with carbohydrate content. The ability of mucous trails to stimulate microalgal growth is correlated with higher total organic content of mucous secretions and an ability to stimulate bacterial growth. A bacterial film may be important in the stimulation effect.

Abstract-The U.S. Environmental Protection Agency (U.S. EPA) protocols for conducting freshwater toxicity tests have been used in California, USA, to evaluate ambient water quality since 1986. Testing evolved from conducting broad watershed surveys for assessing the distribution of toxicity to conducting detailed studies for identifying chemical causes and sources. Using Ceriodaphnia dubia tests, pulses of diazinon toxicity have been detected over a 10-year period throughout California's Central Valley in waters receiving drainage from dormant orchards. In the 1980s, toxicity to C. dubia, caused by methyl parathion and carbofuran in drainage from rice fields, was detected in the Sacramento River. Rice drainage also was toxic to two important local species, larval striped bass and Neomysis. Throughout the state, diazinon and chlorpyrifos toxicity to C. dubia occurs year-round in waters receiving drainage from urban areas. Several years of monitoring the Alamo River in Imperial County with C. dubia demonstrated a recurring seasonal toxicity pattern. Toxicity during a 3-month autumn period was caused by chlorpyrifos and diazinon and during a 2-month spring period by diazinon and carbofuran. Although most toxicity has been detected with C. dubia and linked to insecticides, other examples of toxicity have been identified. Toxicity to Selenastrum has been linked to copper and zinc from mines and to the herbicide diuron in waters receiving agricultural or urban runoff. Ammonia-caused toxicity, originating from dairies and wastewater treatment plants, to fathead minnows has also been identified. Taken together, the results reveal that the three whole effluent toxicity (WET) testing procedures, in association with toxicity identification evaluations (TIEs) and chemical analyses, can be effective for the identification of an array of toxicants originating from several land use practices. In several cases, alternative land use practices or management strategies have resulted in improved water quality as demonstrated by continued toxicity testing.

Samples collected from urban streams in the cities of Sacramento and Stockton, California, USA, during the precipitation season were analyzed for diazinon and chlorpyrifos. Concentrations were determined with enzyme-linked immunosorbent assays specific for each pesticide. Two hundred thirty-one samples from the two cities were analyzed for diazinon; 85% exceeded California Department of Fish and Game water-quality criteria for this pesticide. Chlorpyrifos was measured in 90 of the samples collected from Sacramento and Stockton; 80% exceeded the California Department of Fish and Game criterion for this pesticide. Thirty-six of 47 samples (76.6%) tested for toxicity produced total mortality within 72 h with Ceriodaphnia dubia. Toxicity identification evaluations on selected samples confirmed that toxicity was primarily due to one or both of these pesticides. Uses of diazinon and chlorpyrifos in urban areas include dormant sprays on fruit trees, professional landscape and maintenance uses, and structural pest control. Pesticide concentrations were lower in a catchment favoring commercial and industrial activities compared with a catchment receiving largely residential inputs. Aerial drift from agricultural applications may play a role in storm-water concentrations.