Matthew R. OdenMethodsSourcesTemporal Trends and Spatial Distributions of Polynuclear Aromatic Hydrocarbons (PAHs) in the San Francisco Estuary 1993-2001 Matthew R. Oden Abstract Polynuclear aromatic hydrocarbons (PAHs) can be generated through combustion of fossil fuels, forest fires, and are found in raw petroleum. Some are know to be carcinogenic and mutanegenic. This study was conducted to assess the temporal trends, spatial distributions, seasonal variation, and sediment quality guideline violations of PAHs in surface sediments between 1993 and 2001 in the San Francisco Estuary, CA. Surface sediment samples were collected biannually during the wet and dry seasons from 26 sampling stations and were separated and quantified using gas chromatography-mass spectrometry technique to determine PAH contaminant levels for 14 PAHs. Contaminant levels at some stations consistently violate the National Oceanic and Atmospheric Administration’s (NOAA) sediment quality guidelines. Multiple PAH contaminants were found to be significantly ( alpha <0.05) increasing or decreasing at various sites during the study period. Hydrodynamically similar Bay segments South Bay and Central Bay differ significantly in PAH levels from the Estuary Interface, San Pablo Bay, Suisun Bay, and the Rivers. Seasonal variation is detected and shows that the wet season has higher total PAH contaminant loads than the dry season, which is most likely due to atmospheric deposition of airborne PAH from combustion sources into watersheds that get washed into the Estuary. A multivariate model describes total PAH loadings using the dependent variables segment and percent fines (R2=0.64). The overarching results reveal that some areas of the Estuary have consistent contamination and need more proactive management to confront higher levels of contamination, whereas other parts are showing improvements.Introduction The San Francisco Estuary is roughly 1,600 square miles and receives freshwater through rivers and tributaries that drain a watershed constituting 40 percent of California’s surface area. Twenty million people receive their drinking water from the estuary and 4.5 million acres of farmland are dependent on the water for irrigation. Thirty species of threatened or endangered organisms live in the estuary; while countless other species of fauna, flora, and migratory birds depend on it (SFEI 1999). Large human populations around the San Francisco and Sacramento regions, extensive agriculture in the central valley, and numerous industries lie within the watershed that drains to the estuary. These create a range of pollution problems, as a variety of chemical compounds originating from urban and agricultural runoff, atmospheric deposition, and industrial discharge find their way into marine estuaries (Soclo et al. 2000, Pilar et al. 2003, Tsapakis et. al. 2003). The Regional Monitoring Program (RMP) for Trace Substances monitors concentrations of select toxic trace elements and organic contaminants in the estuary at 26 independent sampling stations (SFEI Fact sheet) (Figure 1). Polycyclic aromatic hydrocarbons (PAHs) are one of the chemical groups that RMP has monitored for 10 years in both surface waters and sediment within the estuary. PAHs are generated through high temperature processing and incomplete combustion of fossil fuel, as well as wood burning (Boehm et al. 1997, Ou et al. 2004). PAH are of special interest because they are persistent organic pollutants that exhibit toxicity, mutagenicity, and carcinogenicity (Oanh et al. 1999, Pilar et al. 2003).Figure 1 (. Map generated using ArcMap showing approximate locations of the Regional Monitoring Program’s sediment sampling locations in the San Francisco estuary.) Sediment is a typical “sink”, where PAH has a tendency to accumulate and concentrate. Intensive industrial activity and dense traffic patterns consistently correlate with high concentrations of PAH in sediments (Ogunfowokan et al. 2003), both of which are present in the SF Bay area. Vehicle emissions contain PAH that become airborne (Dunbar et al. 2001, Marr et al. 2004). One of the principle pathways that PAHs use to enter the estuary is atmospheric deposition, which can occur on the water surface and enter via gas exchange or deposit within watersheds where storm waters convey the contaminants to the estuary (Tsai et al. 2002, Tsapakis et al. 2003). Once in sediment, benthic organisms tend to accumulate PAHs that can be passed up the food web. (Ferguson and Chandler 1998, SFEI 2000, Vinturella et al. 2004). One of the objectives of the RMP is, “to describe patterns and trends in contaminant concentration and distribution” (SFEI 1999). Previous statistical analyses of RMP sediment PAH data have failed to look at changes over time (Daniel Oros 2003, pers. comm.), and were limitedto the nonparametric Kruskal-Wallis one-way ANOVA and the Tukey-Kramer multiple comparisons on ranks of aggregate PAH data (Leatherbarrow et al. 2002). Studies using other sediment data sets have found evidence of increasing levels of PAH in certain areas of the Estuary. Stehr et al. (1997) found total PAH concentrations were increasing at a sampling station near Hunter’s Point in San Francisco between 1984 and 1991, but didn’t uncover any significant trends at five other sampling sites within the estuary. Analyzing the sedimentary record of San Pablo and Richardson Bay, Pereira et al. (1999) determined PAH levels have been increasing since the late 1800’s and that the dominant origin contributing to the current contamination is anthropogenic combustion processes. PAH concentrations in the RMP sediment data are typically compared to National Oceanic and Atmospheric Administration (NOAA) National Status and Trends Program’s sediment quality guidelines effects range low (ERL) and effects range median (ERM) values PAH in sediment and displayed using Delta Graph in publications from the San Francisco Estuary Institute (SFEI 1999, 2000, 2002). NOAA’s sediment quality guidelines relate to the 10th and 50th percentile of concentrations that elicit adverse biological effects in marine organisms (Long et al. 1996). My research focuses on describing PAH contamination in the San Francisco estuary sediment. I seek to identify which stations are consistently violating NOAA’s sediment quality guidelines. Understanding how sediment concentrations of PAH are changing over time (trend analysis) can help
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