Traces Of Household Products Disrupt Sex Genes In Fish Brains

The large, shallow Bay—average depth of less than 30 feet—with hundreds of tributaries, has long been considered by ecologists as a very favorable habitat for fish spawning, hatching and nurseries.

However, scientists of the University of Maryland Biotechnology Institute (UMBI) reported at the annual meeting of the Society for the Study of Reproduction this week that the list of compounds in pollution that can disrupt fish sexual hormones has widened considerably. Compounds in many detergents, plastics, pesticides, some medicines, and even thalates that keep vinyl soft in cars disrupted the sexual development of juvenile zebra fish in experiments at UMBI’s Center of Marine Biotechnology (COMB) in Baltimore.

It has been known for almost 20 years that some environmental chemicals (endocrine disrupting chemicals; EDCs) disrupt reproduction by mimicking natural estrogens. Now, many additional classes of chemicals, functioning as EDCs, are interacting directly with genes that are critical for reproductive success, the scientists reported.

Chemical disruption of a brain gene, which directly affects brain estrogen production, may be a key mechanism for the disruption of the developmental and reproductive capacity of fish. Unlike most animals, many fish produce two forms of a gene responsible for aromatase, an enzyme that makes estrogen--one form in the ovaries, the other in the brain.

“I would not say that it is severe enough that any population is becoming completely monosexed. However, because the Bay is so important as a nursery, chemical-induced perturbations of the reproductive and developmental processes could lead to severe consequences,” said John Trant, COMB associate professor. All of the environmental pollutants were tested at concentrations that can be found in the Chesapeake Bay system.

First, the researchers discovered that the “differential expression of the brain aromatase gene” was associated with sex differentiation. “It became clear that compounds affecting this gene will thereby affect sex and sexual behavior in fish,” concluded Trant. The researchers found that the EDCs regulating gene in the brain can affect more than whether a fish becomes male or female.

“What is dangerous is that in-between stuff,” offered Trant. “You might get males who do not display the correct behavior. In order to mate with a female, he may have to court her, build a nest, chase, or show some form of dominance. So, even if the concentration of these disrupting compounds in the water are not sufficient to completely reverse their sexual physiology, small adjustments in their behaviors would be equally fruitless.”

A growing number of studies have found that when compounds such as polychlorinated biphenyls, dioxins, certain plasticizers, and some detergent additives are in streams or rivers, the fish, birds, frogs and other animals are sometimes all male, or all female, or are partially both sexes in their genitalia. Historically, scientists have suspected actual estrogens or chemicals that mimic estrogens in pollution as the causes of the gender-bending effects on fish. Estrogen (or estrogen-like) molecules dock onto a structure called an estrogen receptor in the cells of the liver, ovaries, fat, breast, brain, bone and many other target tissues in humans. The activated receptor initiates a series of changes into action related to sexual physiology. Many of the pollutants, such as PCB’s, some pesticides and petroleum products in the Chesapeake waters are recognized as estrogen molecules by fish and human cells.

“That’s why scientists have focused there,” said Trant. “But, this is worse than we thought before. This is not simply toxicology. It is interfering with the reproduction of the adults, and potentially skewing sex ratios of the populations.”

The COMB team of Yukinori Kazeto, Allen Place and Trant reported that the aromatase gene expression in zebra fish was changed by multiple classes of pollutants such as estrogen mimics (or xenoestrogens, such as surfactants in detergents and pharmaceuticals), arylhydrocarbons (PAH’s and benzo(a)pyrine), peroxisome proliferators (i.e. pharmaceuticals and plasticizers), and herbicides (atrazine).

Trant said it’s almost certain that the multiple compounds are affecting all the fish in the Bay and beyond, not just zebra fish in the laboratory. (The small zebra fish is widely accepted as an excellent model for fish studies.) “For people looking for a magic bullet of why productivity of the Chesapeake Bay is down, this is not it. There are probably many causes,” commented Trant. “But this is certainly affecting the reproductive health of animals that spawn here and the developmental health of animals that are raised in the Chesapeake Bay.”

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The University of Maryland Biotechnology Institute was mandated by the state of Maryland legislature in 1985 as “a new paradigm of state economic development in biotech-related sciences.” With five major research and education centers across Maryland, UMBI is dedicated to advancing the frontiers of biotechnology. The centers are the Center for Advanced Research in Biotechnology in Rockville; Center for Agricultural Research in College Park; and Center of Marine Biotechnology, Medical Biotechnology Center, and the Institute of Human Virology, all in Baltimore.