The dolphin skimmed down the face of a cresting wave mere feet from where I sat on my surfboard. Then, circling around, it joined up with three friends outside where the waves were breaking. The small pod lingered near Scripps Pier, to the delight of the surfers lined up off the beach, before it moved south along the shore.

It was the third time I’d had a dolphin experience, and it left me flush with adrenaline. A glow stuck with me through the workday. I had recently moved from Juneau, Alaska, to La Jolla, and although I was generally happy with my life in SoCal, at times a vague lethargy had overcome me. But this was a place I could go to feel engaged and rejuvenated. It was about the surfing, but also about the natural beauty and the dolphins.

I don’t think I’m alone in these sentiments. In a typical year, beach visits in San Diego are estimated to be around 20 million, according to the City of San Diego’s Lifeguard Services. But going in the water comes with a risk. The city’s storm drains convey runoff with biological and chemical contaminants into rivers and creeks. Where the creeks flow into the ocean, water quality is suspect, especially after it rains. In addition, every day the City pumps 175 million gallons of treated sewage four and a half miles off Point Loma. In North County, treated sewage is pumped only a mile and a half offshore.

While humans are recreational ocean users, dolphins are exposed to the water 24/7. They cannot leave during the 72-hour water-quality advisory after it rains. Recent scientific research is examining the contaminants in our ocean water, seeking to discover how they affect the health of dolphins and other coastal creatures.

The dolphin that’s seen playing in the San Diego surf — the coastal bottlenose dolphin — is unique in that it resides only in waters close to shore. “Ninety-five percent of coastal bottlenose dolphin sightings are within one kilometer of shore, and the vast majority of these sightings are within 250 meters of the beach,” says Dr. Dave Weller from his La Jolla office at the National Oceanic and Atmospheric Administration. Other dolphins are often found miles offshore. Our local coastal bottlenose population — estimated to be 350 individuals — ranges between Monterey Bay and Ensenada, according to Weller. This makes them vulnerable to human pollution.

“We know that the Southern California Bight is a highly polluted region,” says Weller, referring to the bight — or inward curve in the coast — that begins at Point Conception, just north of Santa Barbara, and continues down to San Diego. For decades, before environmental laws were passed, manufacturers dumped waste containing DDT and PCBs into the Los Angeles sewer system. Tons of these chemicals now contaminate ocean sediment in the L.A. area. “The home of our coastal bottlenose dolphin largely coincides with this hotspot of poor water quality and high levels of pollutants,” says Weller. “This proximity with human activities and development raises a red flag of vulnerability.”

Contaminants settle into ocean-bottom sediments, where they’re taken up by mussels, sea urchins, crustaceans, and other bottom-dwelling organisms. From there, the pollutants proceed up the food chain to fishes and then to dolphins.

Although dolphins are likely vulnerable to pollution, scientists do not know how much the health of San Diego dolphins is affected. To help figure this out, Weller and his colleagues, collaborating with scientists at the Scripps Institution of Oceanography, have collected tissue samples (using a small bow and arrow) from over 30 dolphins swimming in the area between Scripps Pier and Swami’s, in Encinitas. The samples are being analyzed for over a dozen chemical contaminants as well as potentially harmful bacteria. The results should be ready by the end of the year. The samples will be used as a baseline. Any future degradation of the aquatic environment can be tracked via trends in contamination found in the dolphins.

Bottlenose dolphins in other parts of the world, especially the Southeastern United States, show significant levels of many chemicals in their tissues, as do seals, sea lions, elephant seals, porpoises, whales, and sea otters. A study conducted by Dr. Gwen Goodmanlowe of Cal State Long Beach and her graduate student Mary Blasius on stranded harbor seals and California sea lions in Southern California found some of the highest levels of DDT and PCBs ever reported in marine mammals. The levels were above those required to cause adverse health effects. Pacific sardines, Pacific chubs, mackerels, and northern anchovies all have been shown to contain detectable levels of DDT.

Another potential threat comes from bacteria and protozoa from human and domestic animal sources. Some bacterial strains found in marine mammals display antibiotic resistance.

Sea otters living north of San Diego, between Santa Barbara and Half Moon Bay, have washed up onshore showing evidence of toxoplasmosis. Caused by the protozoan Toxoplasma gondii, toxoplasmosis can be transmitted in cat feces, or, as Dr. Patricia Conrad of the UC Davis School of Veterinary Medicine and her colleagues put it, “The most likely source of infection [of sea otters] is by infectious, environmentally resistant oocysts that are shed in the feces of felids and transported via freshwater runoff into the marine ecosystem.” Conrad’s group goes on to say, “Toxoplasmosis is a major cause of mortality and a contributor to the slow rate of population recovery for southern sea otters in California.”

Cat poop is a threat to sea otters? It might seem preposterous, but there are more than 84 million of our feline friends in the United States, according to Euromonitor International, and scientists estimate around 73 million feral cats in our country. The number of California cats is unknown. However, a rough estimate (by the author), based on the land area and population of California, suggests around 14 million cats in the state.

Okay, so cats and sea otters don’t mix. What about dolphins? On the East Coast, Dr. Ronald Fayer of the USDA Environmental Microbial and Food Safety Lab reports, “I found evidence of Toxoplasma infection in 100 percent of the dolphin samples I analyzed from Florida.” Other scientists studying dolphins in the southeastern United States have found a suite of perfluoroalkyl compounds (PFCs), which are used in nonstick kitchenware, paints, polishes, and adhesives, among a wide variety of other applications.

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.”