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CADDIS Volume 2: Sources, Stressors & Responses

energy sources physical habitat hydrology temperature water and sediment quality stormwater runoff wastewater inputs riparian and channel alteration urbanization

Pavement sealants & PAHs

Polycyclic aromatic hydrocarbons (PAHs) are common pollutants in urban streams, resulting from numerous transportation-related sources including oil leakage, vehicle exhaust, tire and brake wear, and pavement erosion. Many studies have shown that these compounds can adversely affect stream biota (e.g., Maltby et al. 1995, Pinkney et al. 2004).

Courtesy of U.S. EPA

Pavement sealants are routinely applied to parking lots and driveways to protect the underlying surfaces, and these sealants can be significant sources of PAHs. For example:

  • PAH concentrations were 65 times higher in runoff from coal-tar seal-coated parking lots versus unsealed parking lots (Mahler et al. 2005).
  • PAH concentrations in stream sediments were 3.9 to 32 mg kg-1 higher downstream of coal-tar seal-coated parking lots versus upstream reference sites (Scoggins et al. 2007).

Scoggins et al. (2007) examined the effect of these sealcoats on benthic macroinvertebrate assemblages. They found that:

  • Average macroinvertebrate densities were two times higher at sites upstream of seal-coated parking lots.
  • Chironomid density decreased at sites downstream of seal-coated parking lots, whereas oligochaete density usually increased.
  • Increases in pool habitat PAH sediment toxicity units between sites upstream and downstream of seal-coated parking lots explained decreases in macroinvertebrate richness and density (Fig 25).

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Figure 25. Regression plot of the decrease in (A) macroinvertebrate richness and (B) density between sites upstream and downstream of seal-coated parking lots, as a function of the increase in PAH equilibrium partitioning sediment benchmark toxicity units (ESBTUs) in pool sediments between those sites. ESBTUs were based on 16 EPA priority PAH pollutants; values > 1 suggest toxicity.
From Scoggins M et al. 2007. Occurrence of polycyclic aromatic hydrocarbons below coal-tar-sealed parking lots and effects on stream benthic macroinvertebrate communities. Journal of the North American Benthological Society 26(4):694-707. Reprinted with permission.

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