| homepage | overview | research | students & staff | researchers | download reports |


Principal Investigator: Daniel Schlenk (UCR)


Summary of Research

Polycyclic aromatic hydrocarbons (PAHs) are common contaminants in sediments of waterways worldwide, including the coastal areas of California (Brown et al. 1998).  Sources include industrial discharges, creosote from treated wood, municipal runoff, as well as atmospheric emissions from incineration and automobile emissions.  PAHs are also introduced into marine systems through accidental spills of fuel oil, crude oil, and other petroleum products, and from non-point sources such as natural oil seeps. 


PAHs tend to adsorb to organic components in sediments, where they can be sequestered.  Although only a portion of sediment-adsorbed PAHs are available to marine organisms in the water column, there is substantial uptake of these compounds by benthic fish through the diet, and direct exposure to sediment.  Benthic invertebrate prey are a particularly important source of PAH exposure for marine fishes, because PAHs are bioaccumulated in many invertebrate species (Varanasi et al. 1989, 1992; Meador et al. 1995).  Consequently, determination of sediment quality criteria for the adverse effects of PAHs on benthic biota is necessary in ecological rich assessments of contaminated areas. 


However, unlike many chlorinated hydrocarbons, which boaccumulate in tissues, PAHs are extensively metabolized in vertebrates such as fishes.  Cellular metabolism of PAHs results in conversion of these hydrophobic compounds into polar, water soluble forms that can be readily excreted from the organism.  Thus, parent PAHs generally do not bioaccumulate in fish or other vertebrates, although metabolites present in food are bioavailable to the consumer (McElroy et al. 1991, James et al. 1991).  This lack of accumulation in fishes prevents accurate measurement of exposure using traditional chemical residue methods of analytical chemistry. 


In addition, the chemical nature of PAHs is also quite complex, as environmental samples rarely possess single compounds, but more likely, have a profile of compounds with varied molecular weights and biological activity.  Each of these compounds display differing biotransformation patterns and accumulation tendencies.  In fact significant differences exist between "urbanized" and "non-urbanized" PAH signatures.  The latter is usually of lower molecular weight and greater mobility (Neff 1985). 


Ecological risk assessment paradigms require accurate assessments of exposure coupled with threshold levels of adverse effects.  Without an accurate estimate of exposure, assessments are difficult and may potentially impair management decisions and regulatory policies toward potential polluters. 



Major Accomplishments

Concentrations of selected high molecular weight PAHs ranged from 0.049-38.6 ug/g (Table 1).  In this particular study, high molecular weight PAHs were considered compounds with 3 benzene rings or more. The 100% COP treatment was dominated by fluoranthene with an average concentration of 1.4 ug/g, followed by dibenzo(ah)anthracene at 7.2  ug/g, and phenanthrene at 4.4 ug/g. All other PAH compounds were under 0.4 ug/g in the 100% COP sample. All samples from control to 1% appeared to have similar total HMW PAH concentrations. Concentrations of LMW PAHs tended to correspond to dilution profiles with the exception of 67% COP treatment where values were slightly lower than the 33% COP concentrations. In the 0.66 to 66 % COP sediments, Acenapthene was the dominant PAH with an average concentrations of 30 ug/g in the 100% COP treatment.


Cytochrome P450 1A analysis showed a similar baseline expression pattern from the control to the 33 % COP sediments, with significant induction at the 66 and 100% COP sediments (Figure 1). P-values were 0.05 for the 66% sediment, and 0.01 for the 100% sediment exposure.


FAC accumulation in bile was variable in the 33, 66 and 100%  PAH sediment exposures, with a trend towards increasing FACs in the bile at the higher sediment concentrations (figures 2 through 4). Values for BAP ranged from 5 to 30 ug/ml, PHE from 33 to 2,300ug/ml, and NAP from 500 to 14,000ug/ml. The lower concentrations of contaminated sediment (0.33%, 0.66%, and 1%) showed a slight trend for increasing PAHs with increases in sediment exposure. Increases in FACs did not correspond directly to increases in PAHs detected in the sediment particularly in the 33 and 66% COP sediments. Metabolites were highest following exposure to the 33% COP sediment, while PAHs were highest at the 100% sediment exposures. Much greater amounts of PAHs were found in the 100% sediments versus the 33% and 66%, and this did not result in a similar increase in FACs.  FACs fluorescing at the PHN and NAP wavelengths were highly correlated, with an r2 of 0.97. BAP values were less related to PHN and NAP, with r2 values of 0.72 and 0.71 respectively.


No significant differences in plasma steroid concentrations between treatment groups and controls were observed (Figure 5).  However, a trend toward reduction of estradiol levels was observed at the 1% COP treatment. Estradiol concentrations were between 347 to 849 pg/ml from the control to the 0.66% COP sediments, and from the 0.1 to the 100% COP sediments the values ranged from 21 to 494 pg/ml. Testosterone levels were lower than estradiol at all concentrations (even control). GSI did not show any significant response to treatment.



Figure 1.  Hepatic cytochrome P4501A expression from male halibut treated with various concentrations of COP sediments.  Each value represents the mean of 4 individuals + SD. *p < 0.05





Figure 2. Biliary phenanthrene-like compounds from male halibut treated with various concentrations of COP sediments. Values with error bars represent the average of 3-4 replicates + SD.





Figure 3. Biliary naphthalene-like compounds from male halibut treated with various concentrations of COP sediments. Values with error bars represent the average of 3-4 replicates + SD.





Figure 4. Biliary benzo(a)pyrene-like compounds from male halibut treated with various concentrations of COP sediments. Values represent the average of 2 individuals.





Figure 5. Plasma steroid and GSI values for male halibut treated with various concentrations of COP sediments. Each value represents the mean of 4 individuals + SD.






Our study found slight induction of CYP1A in response to natural PAH contaminated sediment, and decreased estradiol levels at a lower threshold of exposure than either CYP1A induction or FAC accumulation. In comparison to values seen in other studies, these fish seemed to have particularly variable response in regard to FAC accumulation in bile, which may have been resolved with normalization to biliary protein content. CYP1A induction also seemed low with regard to the amounts of PAHs in naturally contaminated sediment from oil seeps. This may be due to a species specific low induction response, or perhaps natural oil from seeps have different mixture effects than anthropogenically derived PAHs which have previously been shown to cause the response.




| [homepage] | [overview] | [researchers] | [students & staff] | [research] | [download reports] |