Current Research

Characterization of Baseline Bioaccessible Pesticide Loads in the Sacramento Deep Water Ship Channel and the Effects of Turbation on Bioaccumulation: Cristina La

The Sacramento Deep Water Ship Channel (SDWSC) is a man-made canal belonging to the San Francisco Estuary (SFE) that stretches from the Port of Sacramento in West Sacramento, California, USA, to the Sacramento River. While originally constructed with the intent to attract heavy industry alongside its existing agricultural lands, the SDWSC has presently become critical habitat because of favorable nutrient conditions, food abundance, and turbid waters for the endangered fish species Delta smelt (Hypomesus transpacificus). For these reasons, the United States Department of the Interior has proposed to repair or replace the West Sacramento lock system to connect the SDWSC with the main stem of the Sacramento River in hopes of aiding in the recovery of the Delta smelt populations by pushing food resources out of the SDWSC and into the broader North Delta. However, prior to these actions we must consider the potential effects of reintroducing these two systems will have on the remobilization of sediment bound legacy contamination. The aim of my two-year study will be to characterize the bioaccessible fraction of legacy organochlorine pesticides and current use pyrethroid insecticides present in the system to assess whether reintroduction would increase contaminant exposure in the Delta smelt. In addition to the field aspect of this study, there will be a lab portion dedicated to measuring the bioaccumulation of radiolabeled 14C-PCB congener 2,2’,4,4’,5,5’-hexachlorobiphenyl through a series of 10-d static bioaccumulation tests on Daphnia magna under different turbation simulations. This will show how the turbation from the potential reintroduction of the two systems could affect the bioaccumulation of HOCs in the Delta smelt’s food source, zooplankton.

Development of Resistance to Insecticides in Hyalella azteca: Nichole Gamble

Streams, estuaries, and other bodies of freshwater are contaminated with a variety of different insecticides due to runoff from agricultural and urban landscapes. Currently, Hyalella azteca, a non-target epibenthic amphipod, has developed resistance to pyrethroid insecticides due to single amino acid mutations in the voltage-gated sodium channel gene. The degree of resistance in H. azteca is similar to that observed in several target species, including Musca domestica, Cimex lectularius, Blattella germanica, and Rhipicephalus microplus. Yet, the costs associated with the development of resistance include a loss of fitness with reduced reproductive rates, decreased thermal tolerance, and decreased tolerance to salinity. Aquatic systems are often contaminated with several different types of insecticides, therefore there is a possibility that H. azteca have also developed resistance to other classes of insecticides. The aim of my study is to determine if pyrethroid-resistant H. azteca have developed resistance to other insecticides. Three lab-cultured H. azteca populations (a clade C wild-type population, a clade C pyrethroid-resistant population, and a clade D pyrethroid-resistant populations) were exposed individually to the insecticides bifenthrin (pyrethroid), chlorpyrifos (organophosphate), carbaryl (carbamate), DDT (organochlorine), fipronil (phenylpyrazole), and imidacloprid (neonicotinoid) through a series of 96-h water-only acute toxicity tests. I am hypothesizing that pyrethroid-resistant H. azteca have developed resistance to other insecticide classes due to previous long-term exposure, which makes them susceptible to cross-resistance. The development of resistance to additional insecticide classes may suggest additional population-level vulnerabilities in field H. azteca.

Development of a response spectrum model for chlorpyrifos and inland silversides (Menidia beryllina): McKenna Haney

The San Joaquin Bay Delta is an estuary located in Northern California which has been a focus of environmental research for years because of the pesticide contamination. This has led to the decline of the endangered Delta smelt (Hypomesus transpacificus) which is an important health indicator species. My research will use inland silversides (Menidia beryllina) as a surrogate species for Delta smelt to develop a response spectrum model for chlorpyrifos in tissue residues. Those tissue concentrations then can be compared against the response spectrum to predict the toxicological effects expected in these field populations of inland silversides. Sampling inland silversides in the San Joaquin Bay, analyzing their tissue residues, and comparing the values to the response spectrum can be reflected to Delta smelt populations as well.  

Development of a response spectrum framework to assess the effects of pesticide residues in Central Valley salmon: Md Habibullah Al-Mamun

Exposure to contaminants, including several current-use and legacy pesticides is one of the major factors of declining Chinook Salmon, Oncorhynchus tshawytscha, population in the Sacramento-San Joaquin River systems. Pesticide exposure may increase fish mortality risk from direct toxicity, but even at low concentrations, pesticides are known to cause a variety of sublethal impacts on fish, including reduced growth rate, altered behavior, and reductions in sensory perception and overall fitness. Juvenile Chinook Salmon outmigration is further impacted by predation pressures from other species. Laboratory exposures have demonstrated that pesticide exposure can negatively impact overall behavior, olfactory response, swimming performance, and cardio-respiratory function, which would make migrating smolt more susceptible to predation. Pesticide residues commonly bioaccumulate in fish and are often monitored by state and federal agencies, but the potential effects of that body burden remain largely unknown. The relationships between body residues and biological effects, including sublethal effects, are critically important for determining the role pesticides may be having on salmon declines. The proposed study addresses several critical areas of uncertainty related to the role of pesticides in Chinook Salmon population declines, including thresholds of pesticide loadings in salmon tissues that result in sublethal impairments and the effects of pesticide mixtures on these endpoints. Information collected from the proposed study will permit to develop a response spectrum framework that associates measured contaminant residues with adverse biological effects for juvenile Chinook Salmon. This study will allow for direct comparisons of data obtained from routine monitoring activities to a residue-effects framework that will show whether any impacts are expected to occur for that species at a specific dose. It also will guide future management decisions regarding the effects of pesticides on sensitive salmonid species.

Observing the potential for trophic transfer of p,p’-DDT, Bifenthrin, Chlorpyrifos and metabolites to juvenile Chinook salmon (Oncorhynchus tshawytscha) from consumption of Chironomus dilutus: Eleni Robinson

Many populations of Chinook salmon (Oncorhynchus tshawytscha) in the western United States have experienced large declines in spawning numbers in the last decade. In the Central Valley, CA, both legacy and current-use pesticides have been detected in known Chinook dietary items, including the midge, Chironomus dilutus. Both larval and adult midges have been shown to be the most common dietary items for rearing juvenile Chinook in the Sacramento-San Joaquin Delta, however the capacity for contaminant uptake and biotransformation among midge life stages is poorly understood. One of the most commonly detected compounds in Chinook salmon rearing habitat is p,p’-DDT, its isomer, o,p’-DDT, and its biotransformation products, p,p’-DDE and p,p’-DDD. Additionally, the pyrethroid Bifenthrin, organophosphate Chlorpyrifos, and their metabolites will be tested. This study aims to observe bioaccumulation and biotransformation of each pesticide across all life stages of midges, from larvae to flying adults, and assess the potential for trophic transfer to Chinook. Bioaccumulation and biotransformation products will be assessed in Chironomus dilutus and juvenile Chinook, elucidating the potential for trophic transfer of contaminants and risk to rearing juvenile salmon.

Development of response spectrum framework for 4,4′-DDE and bifenthrin using body residues in juvenile Chinook salmon (Oncorhynchus tshawytscha): Katie Knaub

Pesticide contamination in the waters of the Sacramento-San Joaquin River Delta (Delta) has been established as one of the major contributors to Oncorhynchus tshawytscha (Chinook salmon) population declines observed in the last 70 years. My research aims to develop a response spectrum framework for 4,4′-DDE and bifenthrin using body residues in juvenile Chinook salmon. This approach circumvents the issues associated with the application of traditional toxicity test results, which relies on aqueous concentration as a dose metric, to larger environmental systems. Use of chemical concentration accumulated within fish tissue, or body residue, as the dose metric provides a more direct measure of chemical exposure, since route of uptake is not critical to quantification of exposure. One of the goals of this work is to establish a link between biological effects and body residues in Chinook salmon. The resulting framework will be applied to archived Chinook salmon samples collected from several locations throughout the Delta from 2016 and 2017 to understand potential biological effects occurring within historical Chinook salmon populations. This work can be applied to past and future biomonitoring data to characterize and estimate risk of pesticide contamination in the Delta to Chinook salmon populations.

Bioavailability, trophic Transfer and sub-lethal impacts of pesticides on juvenile Chinook salmon in the San Francisco Bay Delta: lab and field studies: Neil Fuller

Chinook salmon, Oncorhynchus tshawytscha, are an ecologically and commercially important anadromous fish species of the San Francisco Bay Delta (SFBD), CA, which have experienced substantial population declines in recent years. Previous studies have indicated presence of pesticides in tributaries of the SFBD that are utilized for juvenile Chinook rearing. However, the fate and transport of pesticides in these habitats, including floodplain and riverine areas, has not yet been examined. Multiple routes of trophic transfer, including dietary sources via benthic and pelagic food webs, have the potential to expose juvenile Chinook to bioavailable pesticides. This research aims to elucidate pathways and trophic transfer of pesticides to juvenile Chinook rearing in both riverine and floodplain habitats of the SFBD, providing fundamental information regarding the potential benefits of floodplain rearing. In addition, laboratory exposures of hatchery-origin juvenile Chinook to diet-borne pesticides will elucidate the sub-lethal impacts of environmentally relevant pesticide mixtures on growth, behavior and neuroendocrinology of juvenile Chinook. This research will ultimately support the management and restoration of endangered salmon populations in the SFBD.

Investigation of pesticide bioavailability and trophic pathway transfer to juvenile Chinook salmon of the San Francisco Bay Delta, California : Sara Anzalone

Chinook salmon are an anadromous salmonid native to the Pacific Coast of North America. Juveniles spend crucial rearing time in freshwater habitats before migrating to the Pacific Ocean to mature. Multiple anthropogenic stressors exist in the freshwater rearing habitats of Chinook salmon of the San Francisco Bay Delta (SFBD), California, including pesticide loadings from large-scale agricultural activities and other non-point sources. Exposure to bioavailable pesticides, through benthic and pelagic trophic pathways, is of critical concern for juvenile salmonids rearing in these habitats. This study focuses on determining the primary pathways of exposure for juvenile Chinook salmon rearing in the SFBD of California. Stable isotope and fatty acid analysis of primary producers, invertebrates and juvenile Chinook salmon (fall-run) of the SFBD will be conducted to infer these pathways. Additionally, concentrations of pesticides will be analyzed in samples representing each trophic level, to determine bioavailability and potential bioaccumulation.

Using Tenax extractions to assess pyrethroid insecticide toxicity in urban sediments: Kara Huff Hartz

Single-point Tenax extractions (SPTEs) have been shown to correlate to the bioaccumulation and toxicity of many hydrophobic organic contaminants in sediments  (Lydy et al. 2015). The use of SPTEs provides a rapid and an inexpensive tool that complements bioassays, biosurveys, and exhaustive chemical extractions for sediment quality assessments. In collaboration with the USGS, SPTEs are used to assess the bioaccessibility of pyrethroids, an important class of contaminant in urban sediments in the northeastern United States. The aim of the proposed work is to measure the pyrethroid concentrations in sediments using Tenax extractions, and to quantitatively evaluate their correlation with standard bioassay endpoints. The established relationships between Tenax extractable concentrations and toxicity can then be used to estimate toxicity in future assessments of pyrethroid contamination.

Phototactic Response in Pyrethroid-Resistant Hyalella azteca: Cristina Ramirez

Hyalella azteca is a species of freshwater invertebrate and a vital component to numerous aquatic ecosystems, serving as a primary food source and an indicator species that highlights environmental issues. Increased pesticide use in agricultural and urban landscapes has caused only H. azteca populations with a genetic resistance to pyrethroid pesticides can survive in their native habitats. Although a population’s resistance enables improved survival to acute exposure of pesticides, the genetic resistance in H. azteca has been linked to reduction in population fitness and genetic bottlenecks. The research conducted explores the possibility of resistance mutations in H. azteca altering phototactic response that are important for predatory avoidance. The recorded responses to light of resistant and non-resistant populations were compared through paired testing. A lightbox table was used for the physical stimulus in the trials. The results from the trials suggest that the non-resistant control populations have noticeably more drastic and faster reactions compared to the resistant populations. This suggests that resistant populations are more likely to be predated upon due to slower reaction times. This has the potential to impact population-level survival of resistant non-target invertebrates as well as increase the potential for trophic transfer of bioaccumulated contaminants to those animals who are higher in the food chain.