Platform Session on the Palos Verdes Shelf Superfund Site: Current Understanding of Environmental Risks

Dozens of scientists and managers gathered at a Special Symposium on the Palos Verdes Shelf (PVS) at the 33^rd Annual SETAC North America Meeting in Long Beach, CA. This session focused on research to better understand the environmental risks associated with the PVS Superfund site and brought together researchers addressing the following areas:

Figure 1. Abalone Cove, Palos Verdes, CA (photo credit: Greg Lyons, Southern California Coastal Water Research Project)

The PVS Superfund site (Figure 1) located off of the coast of Southern California contains sediments heavily contaminated with persistent organochlorine pollutants including pesticides (including dichlorodiphenyl-trichloroethane (DDT) and its breakdown products), polychlorinated biphenyls (PCBs) and other pollutants. As with many contaminated sites, sediments on the shelf continue to be a source of chemicals to the water column and biota living within and above them long after industrial releases have been controlled or ended.

Palos Verdes was designated a Superfund site after Montrose Chemical Corporation's largest DDT manufacturing plant discharged industrial waste through the Los Angeles County municipal sewer system whose outfall lies at the bottom of the ocean, at 60 m depth, offshore Los Angeles (Figure 2). These discharges occurred for decades and, although effluent concentrations have been below detection limits since the 1980s, an estimated 110 metric tons of total DDT and another 11 metric tons of total PCB remain in Palos Verdes sediments (Figure 3).

These contaminants are a risk to wildlife and human health. A natural resource damage assessment lawsuit was settled in 2000 and part of the settlement is an effort to minimize risk and restore the ecosystem. In large part, these efforts have been successful, but some problems remain. While concentrations have dramatically decreased in several sport fish, fish consumption advisories still exist on the Los Angeles coastal margin. California brown pelicans have made a monumental comeback after populations plummeted due to eggshell thinning resulting from DDT bioaccumulation. However, bald eagles continue to struggle and only recently started successful hatching (Figure 4).

Figure 2. Map of the Palos Verdes Shelf (from USEPA, Region 9)

The co-chairs divided the session into two parts to reflect the structure of human and ecological risk assessments. The first four presentations emphasized the exposure to DDTs and PCBs present at the site and their concentrations in the sediments, interstitial waters and water column. The emphasis of these talks was to characterize DDT and PCB water column concentrations and transport around the site. One talk also addressed contaminants of emerging concern (e.g., triclosan, polybrominated diphenyl ethers (PBDEs)) and their concentrations in the sediments. After the break, the session continued with talks discussing adverse effects that may result from contamination at the site. These presentations discussed the bioavailability of contaminants associated with the sediments, possible adverse biological effects to site organisms, the swimming patterns of fish living at or near the site and considerations for conducting a site risk assessment. Other talks were focused on human health risk from consumption of sport fish.

Figure 3. Map of total DDT sediment concentrations on the Palos Verdes Shelf (from US EPA Region 9)

The series of presentations in the session had several important messages. First, for contaminants like PCBs and the DDTs, the sediments serve as a source to the water column and are being transported vertically out of the sediments as well as horizontally across the site. These transport mechanisms include diffusion from the sediments and advective transport in the water column. Palos Verdes has become somewhat of a hotspot for testing and evaluating passive samplers. This rapidly developing technology provides key information for managers deciding on remediation options and timing for implementation at the Superfund site. Emerging contaminants such as triclosan and PBDEs are also present in the sediments. Their temporal distributions in the sediments reflect the positive effects of environmental regulations resulting in reductions in concentrations in recently deposited sediments close to the sediment-water interface.

Testing new technology is one of the focal points for managers. While exposures at the site are becoming better understood, the extent of adverse effects at the site is less known. Methods are under development to get a handle on the bioavailability of DDTs and PCBs to organisms at the site. Research is underway to assess which toxicological endpoints are most sensitive for detecting toxic effects at the site. Innovative fish tracking research is being performed that offers the promise of greatly improving our understanding of how long fish spend foraging at the site and thus are exposed to contaminants. Scientists described using high resolution (± 1 m) tracking devices to map the movement of fishes between the Superfund site and popular fishing locations.

Figure 4. Relationship between decreasing effluent concentrations and breeding success of the California brown pelican and American bald eagle in the nearby Channel Islands (as presented in Setty et al. 2012)

In total, all these efforts to collect data about the PVS Superfund site provide important information that can ultimately be used to reduce environmental risks. The information shared at the SETAC North America Annual Meeting will help US EPA, US Fish and Wildlife, NOAA, as well as state regulators consider their next management steps. One of the proposed remediation plan options is to place a large sediment cap, what might be one of the largest and deepest manmade sediment caps in the world, over the most contaminated portions of the Palos Verdes Shelf. Magnitude of contaminant concentrations, bioavailability for accumulation up the food chain, improved understanding of risks and trajectory of recovery all contribute valuable technical information necessary for these costly management decisions.

Platform Session on the Palos Verdes Shelf Superfund Site: Current Understanding of Environmental Risks

Robert M Burgess, Mark G Cantwell, Loretta A Fernandez of the United States Environmental Protection Agency and Ken Schiff and Keith Maruya of Southern California Coastal Water Research Project