5.4. Polyaromatic Hydrocarbons (PAHs)

5.4.1. Background and Sources: PAHs

Polyaromatic hydrocarbons are a class of over a 100 different chemicals, some of which are carcinogenic. They are often found in the environment in complex mixtures. Sometimes the patterns of distribution of the different types of PAHs can give clues to their sources and fates. They are often subdivided into classes of small, Low Molecular Weight (LMW) compounds, and larger High Molecular Weight (HMW) compounds. The two subclasses of PAHs tend to have different sources, environmental fates, and toxic effects, although there is considerable overlap in their characteristics.

PAHs arise from two major pathways. Pyrogenic (“fire”-generated) PAHs are formed during the combustion of organic matter, including fossil fuels. The PAHs formed by combustion tend to be the HMW type. Petrogenic (“petroleum”-generated) PAHs are also formed naturally and are precursors and components of complex organic matter including oil, coal, and tar. Petrogenic PAH mixtures tend to have more of the LMW type of PAH.

Although PAHs are naturally occurring, large quantities are introduced into the environment by human activities, particularly through fossil fuel handling and combustion. About 80% of PAH emissions are from stationary sources such as power plants, and 20% come from mobile sources such as automobiles and trucks, but the distribution can change with locale. Urban environments have more vehicular-related PAHs than rural or agricultural areas (ATSDR 1995). They may also be introduced into the aquatic environment from creosote in preserved wood, which may be a significant historic source of PAHs in the north main stem of the LSJR.

PAHs are mainly introduced into water bodies by the settling of PAH-laden atmospheric particles into the water, and by the discharge of wastewaters containing PAHs. Spills of petroleum products and the leaching of hazardous waste sites into water bodies are other ways that PAHs enter the aquatic environment.

5.4.2. Fate: PAHs

PAHs have a low affinity for the water phase and will tend to bind to phase boundaries, such as surface microlayers and the surface of particles, particularly organic phases (i.e. organisms and the organic fraction of sediments) (Karickhoff 1981). Once they are in the water, the PAHs tend to settle into the sediments fairly quickly, especially the HMW PAHs. The LMW PAHs also associate with particles, but to a lesser extent. As a result, the LMW PAHs can be transported farther by the river’s tides and currents.

PAHs can be degraded by microbes and broken down by sunlight. Biodegradation accounts for the majority of removal in slow-moving, turbid waters typical of some of the LSJR. Many aquatic organisms can metabolize and excrete PAHs, particularly the LMW types, so the chemicals are not extensively passed up the food chain. However, HMW PAHs can accumulate in fish, amphipods, shrimp, and clams since they are only slowly degraded and reside in fats in organisms (ATSDR 1995; Baird 1995).

The EPA has focused on 17 different PAHs primarily because they are the most harmful, have the highest risk for human exposure, are found in highest concentrations in nationally listed hazardous waste sites, and because there is information available about them (ATSDR 1995). In our analysis of the LSJR sediment data, 13 of the 17 EPA compounds were examined in detail as well as two that are not on the EPA list. These PAHs were selected for study because of the extensiveness of the data, the uniformity of the study methods, and their presence in the LSJR.

5.4.3. Toxicity: PAHs

Although PAH accumulation does occur in organisms from all trophic levels (Carls et al. 2006; Cailleaud et al. 2009), the PAH concentrations do not biomagnify up the food chain (Broman et al. 1990).  High molecular weight (HMW) PAHs are metabolized by most aquatic organisms to some extent; however, vertebrates have a greater metabolizing capacity than invertebrates (Baussant et al. 2001a; Cailleaud et al. 2009). Invertebrates, such as bivalves and polychaetes, are particularly slow to eliminate PAHs (Baussant et al. 2001a; Baussant et al. 2001b). PAH concentrations in several parts of the LSJR continue to be elevated (Section 5.3) as is reflected in the PAH concentrations observed in oysters collected in the LSJR (Section 5.3.4).

Because threshold PAH concentrations in the fish that result in toxicity (critical body residues) of PAHs are relatively constant, acute toxicity in fish is generally thought to be a function of the bioconcentration factor, resulting in narcosis. PAH toxicity occurs in lipids, particularly in the nervous system of fish, resulting in dysfunction (Barron et al. 2002; Barron et al. 2004).  Specifically, the narcosis occurs due to PAH accumulation in the lipid bilayer of a biological cell membrane, which at elevated concentrations may disrupt the membrane integrity and function, leading to depression of the central nervous system (Van Wezel and Opperhuizen 1995; Barron et al. 2002; Escher et al. 2002; Escher and Hermens 2002; Barron et al. 2004).  Although narcosis is reversible, depending on the PAH concentration, it may result in erratic swimming, reduced predator avoidance, and prey capture ability. PAH acute toxicity values (concentrations causing mortality to 50% of the organism; LC50s) range from 5 to 2,140 mg/L, with the HMW PAHs (e.g. benzo(a)pyrene) being most toxic (Neff and Burns 1996).

The chronic toxicity of PAHs is poorly studied.  Donkin et al. 1989 reported a reduced feeding rate and reduced growth in bivalves exposed to PAHs.  Flounder fed a phenanthrene-contaminated diet exhibited decreased levels of 17B-estradiol (Monteiro et al. 2000).  While several studies have suggested deformities and long-term growth and survival effects in fish embryos exposed to low levels of PAHs, the mechanism of toxicity is still unclear (Barron et al. 2004; Incardona et al. 2004).  Sepúlveda et al. 2002 reported the accumulation of both LMW and HMW PAHs in the livers of Florida largemouth bass collected from different locations in the LSJR.  The liver PAH concentrations were highest in the largemouth bass collected from Palatka, followed by Green Cove and Julington Creek, with the lowest concentrations detected in those collected from Welaka.  Largemouth bass with elevated PAH and pesticide residues in their livers had decreased sex hormones.  Furthermore, females had both lower vitellogenin (egg yolk precursor molecule) concentrations and a lower ratio of fish gonad weight to body weight (gonadosomatic index; GSI), which could affect reproduction in the fish (Sepúlveda et al. 2002).

5.4.4. Current Status: PAHs in Sediments

Polyaromatic hydrocarbons were found mostly at concentrations between the TEL and PEL guidelines. Most (~70%) of the samples in the western tributaries, Area 1, and the north arm, Area 2, had PAH concentrations exceeding the TEL, suggesting a low-level stress on sensitive benthic organisms by these compounds (Figure 5.7). The north arm had the most exceedances of the PELs, indicating that adverse impacts on benthic organisms from PAHs in that region are probable.

Figure 5.7
Figure 5.7 Percentage of samples from 2000-2007 with PAH concentrations that exceed Threshold Effects Levels (TEL) and Probable Effects Levels (PEL) for one or more PAHs. Area 1 – western tributaries; Area 2 – north arm; Area 3 – north mainstem; Area 4 – south mainstem. See text in Section 5.2 for data sources.

The toxicity pressure from PAHs was evaluated for each region using all data available since the 2000s. In Figure 5.8, the relative toxicity pressure from each PAH and the cumulative toxic pressure in each region can be compared. The PAHs exert similar overall toxic effects in Areas 1 and 2, but the PAHs responsible for the majority of the effects were different between the two regions, suggesting different sources of PAHs. The north arm, Area 2, is impacted most by acenaphthene (toxicity quotient >1) but fluoranthene, naphthalene, and 2-methyl naphthalene also contribute significantly to the toxicity pressure (toxicity quotient > 0.5).

In Area 1, the western tributaries, anthracene was the largest single contributor to PAH toxicity, while other PAHs exerted similar, low-level effects (Figures 5.8 and 5.9). Within Area 1, the highest levels for anthracene were found in Rice Creek in 2000-2003, with an average concentration nearly ten times the anthracene PEL (89 ppm), as shown in Figure 5.9. Levels near the PEL were also found in the Cedar-Ortega and Trout Rivers. Sediments in the north and south mainstem regions (Areas 3 and 4) had average concentrations between the two guidelines, and were similar in their patterns of PAH contamination. The north arm, Area 2, where the shipping industry is prevalent, sediments had higher proportions of acenaphthene, naphthalene, and 2-methyl naphthalene, LMW PAHs, than the rest of the mainstem.

Figure 5.8
Figure 5.8 Average toxicity pressure of PAHs in sediments from 2000-2007 in the four areas of the LSJR. Area 1 – western tributaries; Area 2 – north arm; Area 3 – north mainstem; Area 4 – south mainstem. See text in Section 5.2 for data sources.
Figure 5.9
Figure 5.9 Average concentrations of anthracene in sediments from 2000-2007 in the four areas of the LSJR and in three streams in Area 1. Sediment quality guidelines for anthracene are shown as dashed lines. Area 1 – western tributaries; Area 2 – north arm; Area 3 – north mainstem; Area 4 – south mainstem. See text in Section 5.2 for data sources.

5.4.5. Trends: PAHs in Sediments

There was extreme contamination of Deer Creek from the Pepper Industries’ creosote tanks near Talleyrand that was documented in 1991 (Delfino et al. 1991a). Creosote is a product of coal tar that is used for wood preservation. While Deer Creek was the worst contaminated site, there were several other hot spots reported over the years for various PAHs. In the late 1980s, there were several sites all along the LSJR that had extremely elevated levels of PAHs, including acenaphthene in the north mainstem, Area 3, at NAS Jacksonville (278 ppb), fluoranthene in Dunn Creek in the north arm, Area 2, (10,900 ppb), and pyrene in Goodby’s Creek (8470 ppb). Most recently, the highest concentrations of naphthalene and anthracene (LMW PAHs) occurred in Rice Creek in 2002.

There are encouraging signs that some PAH levels have gone down since the late 1980s. Data were not collected continuously over the years, but for many PAHs, high concentrations found in the late 1980s declined dramatically to lower levels in 1996 where they have remained at lower concentrations. This pattern was particularly evident in Areas 3 and 4, the north and south mainstem regions (Figure 5.10) and may reflect recovery from the creosote contamination during that time. Some of the PAH load in the western tributaries has also declined since the 1980s.

Figure 5.10
Figure 5.10 Median concentrations of PAHs in sediments from 2000-2007 in Area 3 (north mainstem) and Area 4 (south mainstem). Note that years are not continuous. See text in Section 5.2 for data sources.

However, since the 1990s, several PAH levels may be slowly rising in the mainstem. While there are too few data points for a rigorous trend analysis, there may be a modest increase in most PAHs in Areas 3 and 4, similar to those shown for pyrene in Figure 5.11. Despite the uncertainty due to a lack of data, it is important to continue monitoring locales such as Clay and St. Johns Counties, which are rapidly becoming more urbanized, and can be expected to generate the PAHs typical of those land uses.

Figure 5.11
Figure 5.11 Apparent rise of median concentrations of pyrene in LSJR sediments since 1996 in Area 3 (north mainstem) and Area 4 (south mainstem). Dashed lines represent trend lines. See text in Section 5.2 for data sources.

5.4.6. PAHs in Oysters

In the Mussel Watch Project of NOAA’s National Status and Trends Program (NOAA 2007b), oysters in Chicopit Bay in the north arm, Area 2, of the LSJR were analyzed for PAHs from 1989-2003 (Figure 5.12). These data show that there is a broad spectrum of PAH contaminants in Chicopit Bay oysters, but the PAHs with the most consistently high levels are pyrene and fluoranthene. There is no apparent decrease in the total PAH values in the oysters, despite decreasing trends of other contaminants such as PCBs, some pesticides, and some metals (O’Connor and Lauenstein 2006). In the 2000s, the sediment PAHs in the Area 2 north arm has a distribution similar to oysters with a predominance of fluoranthene, naphthalene and 2-methylnaphthalene. However, the high levels of acenaphthene found in the sediment in the 2000s were not reflected in oyster tissue.

The PAHs in the oysters have many possible sources, but several are often associated with petroleum contamination, a possible result of Chicopit’s proximity to a shipping channel with high boat traffic. This appears especially true in 2003 when the concentrations in oysters approached the levels of the 1980s. The 2003 oysters also had more of the methylated LMW PAHs that suggest petrogenic origins of the compounds. Standards for consumption are sparse for PAHs (EPA 2007), but for the compounds for which there are standards (anthracene, acenaphthene, fluoranthene, fluorene, and pyrene), the levels found in these oysters would not be harmful. However, as noted, there are few direct data about the hazard of consumption of PAHs, including the notoriously carcinogenic benzo(a)pyrene or other PAH carcinogens.

Figure 5.12
Figure 5.12 Concentration of select PAHs in oysters in Chicopit Bay, LSJR (Area 2 – north arm).
Note that years are not continuous. See text in Section 5.2 for data sources.

5.4.7. Point Sources of PAHs and related compounds in the LSJR Region

Reported PAH emissions to the LSJR region atmosphere have dropped by 83% over the last decade, mainly due to reductions in emissions by electric utilities (EPA 2015b). In 2013 the total emitted PAHs was 112 pounds, 100 pounds of which came from the paper industry. Direct surface water discharges of PAHs have declined from nearly 20 pounds in 2001 to a pound in 2013, all of which is now released by electric utilities. Despite the decline in surface water discharges, PAHs represent one of the top ten chemicals that have the highest potential for human health risk of all discharges in the LSJR basin (EPA 2013e).

Overall, there was a significant drop in point source releases of PAHs and related compounds into the air and water in the LSJR region between 2001 and 2013. Several industries have shared in reducing the overall aromatic hydrocarbon loading to the region.

5.4.8. Summary: PAHs

Portions of the LSJR appear to still be recovering from severe creosote contamination from the 1980s, but there are likely to be additional petroleum and combustion sources. The PAHs occur at levels that may be problematic in some areas, and there continues to be widespread contamination. Near the port in the north mainstem, the combined impacts from power plants, shipping, and the maritime industry are likely to cause this region to continue to be the most heavily impacted by PAHs into the future. There is direct evidence that these compounds reside in consumable organisms in the river in that area. There is a possible rise of PAHs in the southern mainstem portion of the river, which may be beginning to suffer the same stress from urban impact that the north mainstem experiences. In summary, PAHs in the LSJR are likely to be a significant source of stress to sediment-dwelling organisms, despite their overall decline since the 1980s. A drop in the release of PAHs into the region by industries since 2001 may affect a gradual improvement in the next few years if the emission rates remain stable or decrease. In the previous report, the STATUS of PAHs in sediments was unsatisfactory while the TREND in the north marine/estuarine section was improving, and the TREND in the south fresh water section was worsening. The STATUS and TREND of PAHs in this year’s report were not updated because of lack of data.

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