At the Southern California Coastal Water Research Project, based in Costa Mesa, Steven Bay and his colleagues have identified a poster child for food-web contamination, a flounderlike fish called the hornyhead turbot. If life on the bottom of the ocean weren’t bleak enough, the hornyhead turbot has our pollution to contend with. Specifically, turbots have been found to bioaccumulate a variety of different man-made chemicals.
In 2006 and 2007, Bay collected tissue samples from the hornyhead turbot, as well as samples of ocean sediment, seawater, and effluent at the outfall of the Point Loma Wastewater Treatment Plant and at three other sewage outfalls off the coast of Los Angeles and Orange counties.
The study looked for and found 85 hormones, industrial/commercial compounds, pesticides, and pharmaceutical/personal-care products in the samples. All the samples of treated sewage contained ibuprofen, naproxen and the lipid-lowering drug gemfibrozil. Among the 37 chemicals found in the hornyhead turbot were Galaxolide (used to scent laundry detergent), three different antibiotics, oxybenzone (sunblock), triclosan (an antibacterial agent found in soaps, deodorants, and trash bags), PBDEs (flame retardants used in clothing and electronics), and DDT. Bay’s group has found evidence that this chemical uptake may disrupt proper endocrine functioning in the flatfish. “We have found some evidence that levels of thyroid hormones are reduced in turbot that carry a higher level of contaminants,” says Bay. “While it is too early to say for sure, there is also evidence of hormone imbalances indicative of chronic stress.”
If all this contamination is too depressing, the news is not all bad. Two of the chemicals found in the fish’s tissue are diazepam (Valium) and carbamazepine, used as a mood stabilizer in humans.
In dolphins, the health effects may be greatest in the babies, according to Dave Weller. Every time a female dolphin gives birth, she transfers contaminants to her calf. “Transfer of contaminants from mother to calf occurs in utero and through the mother’s milk,” says Weller. “Some contaminants may disrupt the endocrine system of the young calves. Other chemicals may have an effect on the immune system.”
California bottlenose dolphins need healthy babies to sustain the population. Weller and his colleagues plan to compare the amount of contaminants found in the nearshore population of dolphins with dolphin populations found in offshore waters. “We hypothesize that the coastal population will have much higher contaminant loads than the offshore dolphins.”
Some consolation can be found in the fact that dolphins are not likely killed outright by pollutants. “There is a public misconception that contaminants can kill marine mammals by themselves,” says Dr. Keith Maruya, one of Bay’s colleagues, “but this is likely not true. However, dolphins and other marine mammals face many risks in their environment that may have a combined effect.” Maruya cites changing ocean climate and domoic acid, a naturally occurring toxin, as environmental stressors that might conspire with contaminants to reduce dolphin survival.
Dr. Kelly Goodwin, at the National Oceanic and Atmospheric Administration, is focusing on the bacterial risk to dolphins. She isn’t convinced that all the observed antibiotic resistance seen in marine animals can be linked to a human source. “Antibiotics are produced by microbes, and bacteria respond by developing resistance naturally. We don’t know enough about these populations to say for sure that all of the resistance comes from human-produced antibiotics,” Goodwin says.
But she doesn’t want to understate the potential for adverse health effects either: “Coastal bottlenose dolphins spend all of their time in the nearshore environment. They are sentinels for environmental health and for our own health.” Goodwin cautions that we need to take care of our nearshore environment: “What rolls downstream can also come back and bite us in the butt.”