Research Areas > Contaminants > Organic Compound Deposition

Project: Atmospheric Contribution of Organic Compounds to Selected Southern California Waterbodies

Background and Objectives

Despite a 99% reduction in mass emissions from point sources, concentrations of many hydrophobic organic compounds (HOC) in coastal waters of the Southern California Bight (SCB) remain elevated. In addition, more than three dozen coastal waterbodies in southern California remain on the State of California’s list of impaired waterbodies for HOCs in the water column, sediment, and/or fish tissue.

Since current use and discharge of HOCs is limited, legacy inputs from bottom sediments and the atmosphere represent potential sources of HOC contamination to these impaired waterbodies. A recent bight-wide survey of sediments in the SCB found that more than 70% of the SCB area was contaminated with anthropogenic organic compounds; the highest concentrations of these compounds were associated with bays, harbors, and estuaries. Few studies have focused on atmospheric inputs of HOCs to coastal waters in southern California.

This study investigated cross-media transport between the sediment and the water column, and the water column and the atmosphere, to understand the role of each compartment as sources or sinks of HOCs.

Status

This project was completed in 2008.

Methods

This study focused on polycyclic aromatic hydrocarbons (PAH), dichloro-diphenyl-trichloroethane (DDT), polychlorinated biphenyl (PCB), and chlordane compounds.

Concentrations of organic compounds were measured in the air, water and sediment at four water-quality impaired sites in southern California, including the Los Angeles Harbor, Ballona Creek Estuary, Upper Newport Bay, and San Diego Bay. These measurements were used to calculate the air/water and sediment/water fluxes at each site.

Findings

• For PAHs, the sediment was a net source to the water column, and subsequently, the water column was a net source to the atmosphere.

• For DDTs, PCBs, and chlordane compounds, the sediment was a net source to the water column.

• For DDT and chlordane compounds, the atmosphere was also a net source to the water column, primarily through dry particle deposition.

• For PCBs, the water column was a net source to the atmosphere through gas exchange.