Toxicity testing evaluates the effects of sediment samples on laboratory test organisms. Amphipods (Hyalella azteca) and midges (Chironomus dilutus) are exposed to the sediment samples following EPA protocols, and their responses (mortality and growth) are recorded at the end of the exposure. Endpoints are measured as percent survival and growth in milligrams. Higher survival and growth indicate sediments are less contaminated and have lower potential to affect resident organisms.
Hyalella azteca is an epibenthic amphipod that is native to California streams. Wild populations have been known to become resistant to anthropogenic chemicals such as pesticides (Weston et al. 2013), but laboratory cultured populations are sensitive indicators of contaminants. In 2015 the midge Chironomus dilutus toxicity test were added to the program at sites with greater urban land use and urban-use contaminants. This midge is also native to California streams and builds tubes from sediment particles. Use of both organisms in tandem provides additional information on sample toxicity. Amphipod toxicity at SPoT sites can be visualized as a heat map to determine which sites are potentially impacted by contaminants. The heat map below shows percent control survival data between 2008 and 2023 and is color coded to show a toxicity gradient where green indicates non-toxic, yellow indicates toxic, and red indicates highly toxic (survival < 38.6%) samples. It also includes the toxicity trend for each site (stable, increasing and decreasing indicated by upward or downward arrows, respectively, and greyed out when the confidence factor, CF, is 95>CF>90).
SPoT sites are located all across California representing nine Regional Water Quality Control Boards. The sites on the heat map are listed, from top to bottom, based on the region in which they are located. Some sites are toxic year after year (e.g., 403STCBQT), some are non-toxic throughout the 16-year monitoring (e.g., 105KLAMKK), and some sites go up and down in their toxicity potential (e.g., 408CGCS06). Interestingly, some sites have unexpected increase or decrease once a while. e.g., 603BSP002 and 911TJHRxx. These data show application of a standard toxicity marker as a temporal screening tool.
Hyalella azteca is an epibenthic amphipod that is native to California streams. Wild populations have been known to become resistant to anthropogenic chemicals such as pesticides (Weston et al. 2013), but laboratory cultured populations are sensitive indicators of contaminants. In 2015 the midge Chironomus dilutus toxicity test were added to the program at sites with greater urban land use and urban-use contaminants. This midge is also native to California streams and builds tubes from sediment particles. Use of both organisms in tandem provides additional information on sample toxicity. Amphipod toxicity at SPoT sites can be visualized as a heat map to determine which sites are potentially impacted by contaminants. The heat map below shows percent control survival data between 2008 and 2023 and is color coded to show a toxicity gradient where green indicates non-toxic, yellow indicates toxic, and red indicates highly toxic (survival < 38.6%) samples. It also includes the toxicity trend for each site (stable, increasing and decreasing indicated by upward or downward arrows, respectively, and greyed out when the confidence factor, CF, is 95>CF>90).
SPoT sites are located all across California representing nine Regional Water Quality Control Boards. The sites on the heat map are listed, from top to bottom, based on the region in which they are located. Some sites are toxic year after year (e.g., 403STCBQT), some are non-toxic throughout the 16-year monitoring (e.g., 105KLAMKK), and some sites go up and down in their toxicity potential (e.g., 408CGCS06). Interestingly, some sites have unexpected increase or decrease once a while. e.g., 603BSP002 and 911TJHRxx. These data show application of a standard toxicity marker as a temporal screening tool.
Amphipod temporal toxicity trends across CA watersheds shown as Hyalella azteca survival. Data sorted as sites from each region (top to bottom, regions 1-9).
While site-specific toxicity is observed, statewide no trends were identified for amphipod Hyalella and midge Chironomus survival. Hyalella growth showed a stable trend between 2008 and 2023. Further, Hyalella survival and growth responses have significant negative correlations with urban land use, indicating increasing toxicity with increasing urban land use. Chironomus growth is significantly increasing statewide and is positively related to agricultural land use.
In the pie charts below, percentages of sites with different toxicity trends are indicated by different colors. Tan and orange indicate elevated toxicity and greens indicate decline in toxicity. Two toxicity markers were utilized (decreased survival and growth) to identify toxicity for each species. The blue wedges range 65-82% across the four charts indicating mostly stable and no observed trends. Toxicity markers are excellent screening tools to prioritize monitoring at the sites with impacted marker response.
