Encyclopedia of Puget Sound

Concerns rise over rogue chemicals in the environment

Drugs like Prozac and cocaine have been showing up in the region’s salmon. But these are just some of the potentially thousands of different man-made chemicals that escape into the Salish Sea every day, from pharmaceuticals to industrial compounds. Now the race is on to identify which ones pose the greatest dangers.

Fluoxetine hydrochloride. Photo: Meg (CC BY-NC-ND 2.0) https://www.flickr.com/photos/disowned/1125134972
Fluoxetine hydrochloride. Photo: Meg (CC BY-NC-ND 2.0) https://www.flickr.com/photos/disowned/1125134972

Rogue chemicals are everywhere that researchers look — from seagull eggs in the Arctic, to trout in high mountain lakes, to blue whales far out in the Pacific Ocean, along with virtually every animal studied in Puget Sound.

Many of these chemicals are found in vanishingly small traces, in the parts per trillion, but they are always nearby, available for uptake into living things and providing a reminder of the 85,000 synthetic chemicals on the market. On any given day, thousands of them flow into local waters. 

In some cases, their impacts have been well studied. Harmful effects of PCBs — polychlorinated biphenyls — were identified before they were banned in the 1970s. But thousands of other compounds are now catching the attention of scientists. With growing alarm, they are discovering that many of these compounds are biologically active in humans and other animals, posing a variety of health problems.

Among the chemicals of emerging concern are certain pesticides, medicines, cosmetics, soaps, plastics, household products and industrial solvents. Gaining increasing attention is a group of mysterious and difficult-to-study compounds that play havoc with the body’s own internal chemistry.

Consider these findings:

  • Even though many toxic flame retardants have been banned or phased out, residents of the Puget Sound region are retaining these chemicals in their blood, causing potential health effects that remain largely unknown.
  • Compounds that mimic female hormones are continually discharged from wastewater treatment plants into Puget Sound, where some chemicals could be shifting reproductive timing in salmon and flatfish, potentially reducing their reproductive success.
  • Human anti-depressant drugs have been found in salmon and other fish at levels that could be changing their behavior and perhaps their ability to escape predators or find food.
  • Anti-depressants also have been found to alter the day-night cycles of amphipods, tiny shrimplike creatures that play a key role in the food web. These drugs can cause them to swim to the surface during the day, a time when they should be hiding out in deep water to escape predators.

As research continues, biologists and toxicologists in Puget Sound and across the country are trying to decide which compounds should get the most scrutiny, given limited research dollars.

Chemicals that have been identified in Puget Sound were discussed during special sessions at the 2016 Salish Sea Ecosystem Conference last April in Vancouver, B.C., where scientists considered the latest findings — including effects on humans and sea life.

New studies of flame retardants

One group of toxic chemicals, polybrominated diphenyl ethers, or PBDEs, was commonly used to reduce the risk of fire in a variety of household products. Many PBDEs have been banned or phased out, but they are still found at varying levels in nearly every creature on Earth.

A study discussed at the conference involved 113 workers in commercial fishing, electronic recycling and general office occupations. All had measurable levels of PBDEs in their blood, although most of the levels were low, according to Irv Schultz, a research scientist at Battelle’s Pacific Northwest National Laboratory.

A record of their dietary choices showed that people who ate the most fish — more than five servings per week — had the highest levels of PBDEs. Electronic equipment recyclers, who generally consumed less seafood, had the next highest levels of PBDEs, followed by general office workers. Dust from electronic recycling sites also contained notable levels of PBDEs, particularly the chemical formulations used in electronic equipment.

Related article

Room fire simulation shows burned furniture. Photo: Kecko (CC BY 2.0) https://www.flickr.com/photos/kecko/3648477592/Efforts to reduce fire hazards over a half century ago have left an unintended trail of persistent environmental contaminants from flame retardant chemicals known as PBDEs. Bans and substitutes are still evolving.

Effects on brain cells

Other findings, consistent with studies elsewhere, suggest that PBDEs may be disguising themselves as thyroxin and related thyroid hormones, which exert control over a multitude of body functions. Chemicals that mimic hormones or block their action can set off a sequence of reactions in the endocrine system, thus they are known as endocrine disrupting compounds, or EDCs.

Although the biological actions of PBDEs are not well understood, research on animals suggests that they may reduce thyroid hormone levels in the blood, which can result in abnormal brain and nerve development. In humans, low thyroid levels during fetal development are linked to mental impairment, while both low or high thyroid levels seem to alter brain development through childhood.

Levels of PBDEs found in humans and animals in the Puget Sound region may not be a major issue for adult age groups, Schultz said. But increasing attention is being focused on long-term effects resulting from exposure during early development. In mice, for example, even relative low-dose exposure at critical times can result in deficits in learning, memory and sensory development, a condition that grows worse with age.

In a competitive world of prey and predators, brain impairment from chemical exposure can increase the risk that an animal will be eaten or be unable to find its next meal, either one with deadly results, experts say.

Other studies have shown that PBDEs may be passed from mother to child during pregnancy, the most formative stage of life. Children also pick up more contaminants than adults, both through breast milk and through hand-to-mouth exposure to household dust.

PBDEs often escape into the environment by attaching to dust particles. Also, when clothing and other fabrics are washed, the compounds can pass from the wash water into a sewer, through a sewage treatment plant and out into marine waters.

Raw sewage flows into the Tacoma Central Wastewater Treatment Plant. Photo: Kris Symer (CC BY-NC-ND 4.0)
Raw sewage flows into the Tacoma Central Wastewater Treatment Plant. Photo: Kris Symer (CC BY-NC-ND 4.0)

Not surprisingly, this has consequences for many Puget Sound species in addition to humans. A long-term study of harbor seals in the Salish Sea showed that their PBDE levels doubled every three years from 1984 to 2003, but have leveled off or declined since then. Because seals are high-level predators, they incorporate PBDEs from numerous species of fish as well invertebrates, providing an “integrated contaminant signal” for the entire Salish Sea food web, according to the study’s lead author, Peter Ross of Vancouver Aquarium, who was with Canada’s Department of Fisheries and Oceans at the time of the study.

At the Salish Sea conference, Laurie Niewolny of the Washington Department of Fish and Wildlife reported that PBDEs had declined in four different Puget Sound herring stocks from 1998 through 2013. In contrast, the trend for English sole, a bottom fish, was an increase in some areas and a decrease in others.

The general decline in PBDE levels likely resulted from regulatory and voluntary efforts to ban the chemicals, starting with the more toxic forms. Still, the complex chemistry of these compounds can complicate longtime effects on the food web. For example, less-toxic forms of PBDEs, which were manufactured in far greater quantities, have been found to break down in sunlight or during metabolic processes to create more toxic, longer-lasting forms.

The pharmaceutical front

While biological activity turned out to be an unexpected side effect of flame retardants, altering biological activity is the sole purpose of many man-made drugs. The trouble with pharmaceuticals is that some of them escape into the environment — often in tiny amounts through wastewater — where they can disrupt the endocrine systems of non-target species.

A widely reported problem in both fresh and marine waters is the number of male fish with female characteristics, such as oocytes in the male reproductive organs. Oocytes are the precursor cells that develop into an egg. This so-called “feminization” of male fish is believed to result from exposure to female hormones during critical stages of early development.

Synthetic estrogens, used in human birth-control pills, can be found in waterways where they have been discharged with treated sewage after passing through a woman’s body. Other synthetic compounds — including bisphenol-A, a chemical used in plastics, have been found to mimic the effects of estrogen.

Birth-control pills. Photo: UC Irvine (CC BY-NC-ND 2.0) https://www.flickr.com/photos/ucirvine/8137526399
Birth-control pills. Photo: UC Irvine (CC BY-NC-ND 2.0) https://www.flickr.com/photos/ucirvine/8137526399

Laboratory studies suggest that reproductive success is often reduced among these “intersex fish” — males with female reproductive characteristics. Besides the formation of oocytes, intersex fish may have reduced numbers of sperm or sperm of poor quality. Some defects, such as deformed or missing sperm ducts, can render them sterile.

An experiment conducted in Ontario, Canada, took the investigation into feminization to a new level by studying fish populations in near-pristine lake devoid of pollution. For three years, researchers applied synthetic estrogen to the lake to maintain a concentration equivalent to what might be found near the outfall of a sewage treatment plant.

After the second year of treatment, the entire population of fathead minnows in the lake had collapsed due to reproductive failure, according to lead researcher Karen Kidd of the University of New Brunswick. A nearby lake, left untreated, showed no significant problems.

Fathead minnows, a short-lived species, were nearly extinct in the experimental lake at the end of three years, although the population of a longer-lived species of minnows, called pearl dace, was able to survive. Still, all the male fish in the lake — including adult trout — were effectively “feminized,” as revealed by their unnatural ability to produce vitellogenin, a protein that helps eggs develop. Vitellogenin, which the liver produces in response to estrogen, is not found in males under normal conditions.

Since vitellogenin is normally produced only in females, finding this protein in males is now considered a reliable test for the presence of estrogens or structurally related compounds.

In a study of 16 sites around Puget Sound, a research team led by Lyndal Johnson of NOAA’s Northwest Fisheries Science Center found vitellogenin in male English sole at 10 of the sites. The highest percentage of affected fish — 47 percent of those sampled — was at the north end of Seattle’s Elliott Bay. At other Elliott Bay sites, male fish with vitellogenin ranged from 12 to 38 percent.

Outside of Elliott Bay, the highest percentage of male fish with vitellogenin were found in Tacoma’s Thea Foss Waterway, with 22 percent, followed by Port Gardner near Everett, 19 percent; Central Puget Sound near Blake Island, 17 percent; Port Susan in northern Puget Sound, 7 percent; and Bremerton’s Sinclair Inlet, 6 percent.

Out of nearly 3,000 English sole examined, only two intersex fish were found — one male with female characteristics and one female with male characteristics. But the study may have revealed another major issue of concern. In places like Elliott Bay where the percentage of males with vitellogenin was high, the females seemed to have an altered reproductive cycle. Instead of releasing their eggs in the normal February-to-March time period, these females delayed their releases until April or May. This kind of delay could lead to egg fertilization during a time when environmental conditions are less conducive to survival, according to the report.

Louisa Harding, who recently received her doctoral degree from the UW, worked with experts in multiple labs in the Puget Sound region to examine how estrogen and estrogen-like compounds affect the pituitary gland in juvenile coho salmon. The pituitary, a pea-sized body at the base of the brain, is sometimes called the “master gland” for its role in regulating all sorts of hormones.

“The pituitary acts like an operator,” Harding said. “Phone calls that come into the brain get diverted to all the different target tissues.”

Harding discovered that early exposure to synthetic estrogen altered the release of key hormones involved in sexual maturation in coho. At the same time, changes were observed in proteins related to an internal circadian clock, which regulates the timing of hormonal activity and ultimately reproduction.

Tests using effluent from select sewage treatment plants in the Puget Sound region revealed similar endocrine-disrupting effects on the pituitary. Since coho are migrating into saltwater during a critical stage of sexual development, her study and others raise obvious questions about how urban waters may impair salmon reproduction.

Anti-depressants unleashed

If anti-depressants, such as Zoloft and Prozac, can reduce anxiety and alter people’s behavior, what happens when fish and other marine species are exposed to these chemicals, commonly found in sewage effluent?

Both Zoloft (generic name sertraline) and Prozac (generic name fluoxetine) act in a precise way to block the uptake of serotonin in nerve cells, which affects how the brain sends and receives messages. Thus these drugs are known as selective serotonin reuptake inhibitors, or SSRIs. They are often found in sewage effluent at relatively low levels.

In a study of 150 compounds tested from three urban bays in Puget Sound, researchers discovered Prozac (or its equivalent) at detectible levels in both juvenile Chinook salmon and sculpins, according to Jim Meador, a researcher with NOAA's Northwest Fisheries Science Center. Zoloft (or its equivalent) was found in Chinook salmon.

Juvenile Chinook salmon. Photo: Roger Tabor/USFWS (CC BY 2.0) https://www.flickr.com/photos/usfwspacific/6093344388
Juvenile Chinook salmon. Photo: Roger Tabor/USFWS (CC BY 2.0) https://www.flickr.com/photos/usfwspacific/6093344388

Working together, along with a similar compound called norfluoxetine, it seems likely that these chemicals can accumulate in the brains of fish at a high enough level to have an effect, Meador said. Based on other studies, these antidepressants could slow the reaction time of predatory fish and inhibit their ability to capture prey, with potential consequences for their survival, he noted.

Some researchers dispute that the levels of antidepressants found in the environment are high enough to change the behavior of fish, but even lower levels could produce effects that are difficult to measure. Studies will go on, but it could take decades before researchers describe the full effects of a drug on thousands of organisms in Puget Sound.

In amphipods, for example, antidepressants may exert a powerful influence on their daily rhythmic behaviors. Many of these tiny shrimplike crustaceans swim up to surface waters at night to feast on plankton. During the day, they descend into the dark depths to escape predators.

But exposure to antidepressants like Zoloft and Prozac can cause amphipods to swim faster and head into perilous surface waters even during daylight hours, according to several studies of the phenomenon. These effects can be triggered through internal photoreceptors and complex biochemical pathways with drug concentrations found in typical urban waterways.

Because antidepressants are so readily found in marine waters, they could be affecting a multitude of creatures and perhaps the entire food web. Increasing research is being focused on how these drugs may affect the many biological functions influenced by serotonin, the neurotransmitter that helps regulate reproduction, metabolism, immune function, behavior and cycles of life.

Growing ailments

A rise in man-made chemicals being produced and escaping into the environment over the past 50 years has been accompanied by increasing health problems in the human population. Growing ailments include thyroid deficiency, type II diabetes, obesity, early-onset of puberty in girls, reduced sperm count in men, and increased breast, prostate and testicular cancers. Also notable are an apparent increase in neurodevelopmental disorders, such as autism and attention deficit disorder.

While evidence is growing, many of the apparent connections between endocrine disrupting compounds and human disorders have not been fully explained. For that reason, researchers around the world are working to better understand how modern chemicals become entangled in biological processes.

Because some hormones can affect multiple systems and even feedback to maintain their own levels, some EDCs may trigger biological effects at both low doses and high doses, yet they seem to have little effect at midlevel doses. Toxicologists can no longer rely on the idea that higher doses will yield greater biological effects. They’ve also learned to avoid old assumptions about “threshold doses” — the level below which no effects are seen.

As if the issue were not complex enough, one of the great challenges of the future is to study the ongoing effects of multiple chemicals working together, according to The Endocrine Society, a group of researchers, medical doctors and educators who published a 150-page “scientific statement” on EDCs last year. In real life, humans and other affected species are not exposed to just one compound at a time.

“It simply is not reasonable to assume a chemical is safe until proven otherwise,” states the report. “Clearly, not all chemicals are EDCs, but substantial information needs to be provided before inclusion of a new compound in a food storage product, a water bottle, or a household product.”

That goes for replacement compounds as well, the paper says. An example is bisphenol S, which was pushed into production when experts found that bisphenol A, used in plastics, could act like estrogen, causing potential adverse effects during early development. The U.S. Food and Drug Administration banned the use of BPA in baby bottles.

“The BPA substitute, bisphenol S, is now shown to have endocrine-disrupting activity on par with BPA in experimental studies,” according to The Endocrine Society document — although much controversy remains over the effects of BPA at normal exposure levels. Some states have taken action to ban BPA beyond the federal prohibition involving baby bottles.

Because the health effects of so many chemicals are yet unknown, various groups of researchers and medical professionals have called for increased studies into the effects of endocrine disrupting compounds. Some have even offered suggestions about setting priorities for analyzing the effects of the 85,000 chemicals on the market.

Pharmaceuticals, which have been tested in human drug trials, should raise alarms when found in significant levels in the environment, experts say. One approach is to identify concentrations of drugs in marine waters likely to have biological effects on fish. The approach uses existing human studies and conversion factors, such as a drug’s ability to accumulate in fish tissue.

Setting priorities

In 2015, a group of scientists from various agencies in the Puget Sound region developed a “prioritization framework” to help guide future studies into contaminants of concern in Puget Sound [Editor's note: our parent group the Puget Sound Institute was also involved with creating this framework]. Priorities should focus on chemicals that are most likely to cause harm. That involves an assessment of the levels of a contaminant found in local waters as well as the chemical’s known effects on marine life, the group said.

Monitoring also can be important when a biological effect is observed but the cause has not been identified, according to the report published by the Puget Sound Ecosystem Monitoring Program.

This report will be valuable as funding agencies decide which studies involving chemical exposures should come first, said Sandie O’Neill, a biologist with the Washington Department of Fish and Wildlife and a member of the committee.

Since 2008, a combined program of the EPA, the National Institutes of Health and the Food and Drug Administration has been using a high-tech system, involving robots and cell cultures, to rapidly screen 10,000 chemicals for biological effects. The project, still being refined, is called Toxicology Testing for the 21st Century, or Tox21. The program promises to identify the most dangerous compounds for further testing.

More broadly, in June of this year, President Obama signed into law an update to the Toxic Substances Control Act, now called the Frank R. Lautenberg Chemical Safety for the 21st Century Act. Under the revised law, a new chemical must be approved as safe by the Environmental Protection Agency before it can go on the market. Chemicals already on the market must undergo an evaluation to determine if they pose a high or low risk to people and the environment. High-risk chemicals will go through more extensive evaluations to determine which ones pose an “unreasonable risk.” Evaluations must take into account vulnerable populations with no consideration of cost. Formal actions by the EPA, including bans and restrictions, may consider costs and replacement chemicals.

The new law sets out deadlines — including a requirement to have 10 risk evaluations underway by Dec. 22.

Related story

Industrial plant. Photo: Gray World (CC BY 2.0) https://www.flickr.com/photos/greyworld/6159264209New federal legislation, approved overwhelmingly by the U.S. Congress in December 2015 and signed into law by President Obama in June 2016, is designed to make sure that people and the environment are not harmed by new and old chemicals on the market.

Not just cancer

As recently as the mid-1900s, it was generally believed that if a person exposed to a chemical didn’t get sick, then no harm was done, said Irv Schultz, a research scientist with Battelle’s Pacific Northwest National Laboratory. Chemically induced illness was considered a short-term problem.

“We can see how naïve that is,” Schultz said, “but the idea was that if you didn’t die, then in a few days you would be fully recovered.”

That thinking changed over time as medical experts came to realize that exposure to certain chemicals greatly increased the risk of cancer, a disease that often begins in the hidden recesses of the body and may not emerge for years. .

“The disease could be going on for five, 10 or 20 years before someone tells you that you have only a few months to live,” Schultz noted.

Today, as cancer research continues, there are new concerns. Scientists are exploring the subtle effects of man-made chemicals on growth and development, brain function, immune response and reproductive success. In some cases, even small chemical concentrations can trigger a sequence of hormonal responses, which can be difficult to measure yet have profound consequences for the individuals affected — and sometimes their offspring.

In living creatures, some of the most important biological functions depend on an internal communications network that uses natural chemicals — hormones — to send messages from one organ to another. The orchestrated release of various hormones helps to maintain an intricate balance of bodily functions.

The endocrine system, which includes hormone-releasing organs, not only keeps the body working smoothly, it also helps regulate growth, reproductive cycles, perception and emotions, among other things.

Some man-made compounds are known to mimic natural hormones, while others block their activity. Chemicals that have such effects are called endocrine disrupting compounds, or EDCs. When EDCs increase or decrease hormonal activity, the result can be developmental problems, reproductive failure, immune suppression or cognitive difficulties.

Foreign chemicals enter the body when people eat contaminated food, breathe contaminated air or come into direct contact with chemicals. Some mimic the body’s hormones, while others block hormonal function in one way or another.

Because natural hormone levels are constantly changing, it is not easy for researchers to precisely measure the effects of biologically active compounds on humans or other animals. Still, researchers continue to uncover the ways that chemicals can disrupt the endocrine systems of animals throughout the Puget Sound region.

Human endocrine system

Organs involved in the endocrine system produce the hormones that regulate a multitude of biological processes from conception to death. That includes growth, brain development and function, metabolism and reproduction, all acting in concert with each other.

Human endocrine system. Diagram: Kris Symer/PSI
Human endocrine system. Diagram: Kris Symer/PSI   View full-sized image

Hypothalamus: A part of the brain, the hypothalamus is the primary connection between the brain and the rest of the endocrine system via the pituitary. Metabolic processes that are largely automatic, such as body temperature, thirst and fatigue, are regulated through the hypothalamus.

Pituitary gland: Sometimes called the “master gland,” the pituitary is a pea-sized structure that takes signals from the hypothalamus and releases a variety of hormones, which in turn trigger hormone secretion in other endocrine glands.

Thyroid gland: Located at the front of the neck, the thyroid gland releases hormones that affect the body’s metabolic rate, protein synthesis and blood-calcium levels. A release of thyroid hormones increases the burning of fat and glucose, boosts the heart beat and raises the breathing rate. During fetal development, thyroid hormones play a critical role in brain maturation.

Pineal gland: A tiny gland in the brain, the pineal’s primary function is to produce melatonin, which helps regulate sleep patterns. The pineal gland may also contribute to the release of sex hormones by the pituitary gland, which regulates reproduction.

Thymus gland: Important in early development, the thymus stimulates the production of T cells, important to a body’s immune response. After puberty, when T cells have reached an adequate number, sex hormones begin to shut down the thymus, which continues to atrophy through adult life.

Pancreas: Key to maintaining blood-sugar levels, the pancreas secretes glucagon when glucose levels are low, causing the liver to release glucose into the bloodstream. When glucose levels are high, the pancreas secretes insulin, which signals the cells to take up glucose from the bloodstream.

Adrenal glands: Located above the kidneys, adrenal glands produce a variety of hormones. They include glucocorticoids, which stimulate the production of glucose in the liver among other things; adrenaline, which triggers a rapid increase in breathing and heart rate; and androgens, which are male sex hormones.

Ovaries: Besides producing eggs, the ovaries secrete estrogen, testosterone and progesterone. Estrogen is responsible for sexual maturation in females and maintenance of reproductive organs. Progesterone prepares the uterus for pregnancy and helps regulate reproductive cycles. In women, small amounts of testosterone can regulate mood, bone growth and other conditions.

Testes: Besides producing sperm, the testes produce mainly testosterone, critical to the development of male reproductive organs, sexual maturation, maintenance of male characteristics and sperm production. Men also produce low levels of estrogen and progesterone, which help with sexual function.


Full-text available

EDC-2: The Endocrine Society's Second Scientific Statement on Endocrine-Disrupting Chemicals (2015)

Minireview: Endocrine Disruptors: Past Lessons and Future Directions, Molecular Endocrinology (2016).

State of the science of endocrine disrupting chemicals – 2012, World Health Organization (2013)

Toxic contaminants in juvenile Chinook salmon () migrating through estuary, nearshore and offshore habitats of Puget Sound, Washington Department of Fish and Wildlife (2015)

Xenoestrogen exposure and effects in English sole (Parophrys vetulus) from Puget Sound, WA (PDF), Aquatic Toxicology (2007)

Do chemically contaminated river estuaries in Puget Sound (Washington, USA) affect the survival rate of hatchery-reared Chinook salmon? Canadian Journal of Fisheries and Aquatic Sciences (2014).

Dietary Exposure to 2,2′,4,4′-Tetrabromodiphenyl Ether (PBDE-47) Alters Thyroid Status and Thyroid Hormone–Regulated Gene Transcription in the Pituitary and Brain, Environmental Health Perspectives (2008).

The Consequences of Feminization in Breeding Groups of Wild Fish, Environmental Health Perspectives (2011).

Collapse of a fish population after exposure to a synthetic estrogen, Proceedings of the National Academy of Sciences (2007)

Developmental Exposure to Polybrominated Diphenyl Ethers and Neurodevelopment, Current Environmental Health Reports (2014).

Lactational Exposure to Polybrominated Diphenyl Ethers and Its Relation to Social and Emotional Development among Toddlers, Environmental Health Perspectives (2012).

Polybrominated Diphenyl Ether (PBDE) Levels in an Expanded Market Basket Survey of U.S. Food and Estimated PBDE Dietary Intake by Age and Sex, Environmental Health Perspectives (2006).

Contaminants of Emerging Concern: A Prioritization Framework for Monitoring in Puget Sound (PDF), Puget Sound Ecosystem Monitoring Program (2015).

Flame Retardants: A Report to the Legislature (PDF), Washington State Department of Ecology (2015)

High-Throughput Toxicity Testing: New Strategies for Assessing Chemical Safety, Food Safety (2016)

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Contaminants of emerging concern in a large temperate estuary, Environmental Pollution (2016).

Neural defects and cardiac arrhythmia in fish larvae following embryonic exposure to 2,2′,4,4′-tetrabromodiphenyl ether (PBDE 47), Aquatic Toxicology (2007).

Behavioural and transcriptional changes in the amphipod Echinogammarus marinus exposed to two antidepressants, fluoxetine and sertraline, Aquatic Toxicology (2013).

Declining concentrations of persistent PCBs, PBDEs, PCDEs, and PCNs in harbor seals () from the Salish Sea, Progress in Oceanography (2013).

About the Author: 
Christopher Dunagan is a senior writer at the Puget Sound Institute.