Fate and Transport of Hydrophobic Organic Contaminants in the Sacramento Deep Water Ship Channel

Author

Cristina La, Southern Illinois University CarbondaleFollow

Date of Award

5-1-2025

Degree Name

Master of Science

Department

Zoology

First Advisor

Lydy, Michael

Abstract

The Sacramento Deep Water Ship Channel (SDWSC) is an important habitat for multiple species that have been declining in population in the California Delta such as delta smelt and longfin smelt. Currently, both populations are just a fraction of what their populations used to be in the 1970’s and have shown minimal signs of recovery. Multiple factors have been attributed to their decline in populations such as channelization, lack of freshwater flow, nutrient limitations, and contamination, yet in important habitat such as the SDWSC, the understanding the risk aquatic organism have to contaminant exposures is minimal. To understand what types of contaminants are present in the channel and the chemical partitioning in the environment, we analyzed 66 hydrophobic organic contaminants (HOCs) in multiple environmental matrices including total sediments, zooplankton, and suspended solids, and ran Tenax extractions on a subset of sediment samples to estimate the bioaccessibility of the sediment-associated compounds. Samples were collected from six different sites spread longitudinally across the channel. To understand the effects of ship-induced resuspension on contaminant exposures, we also collected samples at one site on the SDWSC closest to the Port of West Sacramento and sampled before and after three ships passed through the site. Turbidity measurements and total suspended solids (TSS) were collected during each sampling event. For the longitudinal sampling, no overlying significant differences in concentrations per site were observed, however the northern sites and southernmost site tended to have higher concentrations of polyaromatic hydrocarbons (PAHs). 4,4’-dichlorodiphenyldichloroethylene (DDE), phenanthrene, fluoranthene, pyrene, benzo[a]anthracene, and chrysene were found in every sample. The highest contaminant concentrations were extracted from the suspended solids, with PAHs being the most prevalent class of compounds. Bioaccessible concentrations of organochlorine pesticides (OCPs), pyrethroids, and PAHs were extracted from the sediments, showcasing a risk of contaminant uptake to aquatic organisms. The highest concentrations of four compounds extracted from the sediments exceeded sediment quality benchmarks, however despite sediments exceeding sediment quality benchmarks, the suspended solids-associated contamination were significantly higher than what was extracted in the sediments, which indicates that the water column may be more of a concern than the bed sediments. For ship traffic sampling, turbidity measurements after ship passage were significantly higher. TSS concentrations increased after ship passage, with a significant increase after the second ship. Total sediment concentrations decreased after the passage of the second ship, as well as the bioaccessible concentrations after the second or third ship, but these trends were not reproducible across the different sampling events. The inconsistencies in effect of contaminant concentrations may show that effects are ship-specific, and that the lack of overall change may show that individual ship passage contributes to the maintenance of steady state in the system. The compounding effect of frequent ship activity is more of a concern than the effects of individual ship passage.