By Peter Montague
In the early 1990s, British researchers at Brunel University in Uxbridge noticed that male fish living downstream from a sewage treatment plant near London had testes laden with eggs. The male fish had become hermaphrodites (also known as intersex — having the sexual characteristics of both males and females).
Subsequently, when caged trout were placed downstream from sewage treatment plants in several British rivers, the males were discovered to have elevated levels of a protein called vitellogenin in their blood. Vitellogenin is the protein responsible for making egg yolks in female fish.
Ordinarily, little, if any, vitellogenin is found in male fish. Male fish have a gene which, if triggered by oestrogen (female sex hormone) can produce vitellogenin, but male fish ordinarily lack sufficient oestrogen to trigger that gene.
British researchers John Sumpter and Susan Jobling then reported that male trout caged downstream from sewage treatment plants throughout England showed the telltale vitellogenin in their blood, indicating that something coming out of sewage treatment plants was having an oestrogenic effect on the fish.
The British researchers tested a few common industrial chemicals to see if they could stimulate the production of vitellogenin in male trout under laboratory conditions. They found that several common industrial chemicals could do the trick, and could do it in a dose-dependent way: the more chemical the male trout were exposed to, the more vitellogenin they produced.
Chemicals found to induce vitellogenin in males included octylphenol and nonylphenol (both alkyl phenols, which are commonly used in detergents, toiletries, lubricants and spermicides); bisphenol-A (the building block of polycarbonate plastics); DDT (the common pesticide, banned in the US but still widely used in some parts of the world); and Arachlor 1221 (one of the 209 varieties of PCBs, or polychlorinated biphenyls —common industrial chemicals now banned in the US but still widely found in the environment).
The same researchers then tested mixtures of these chemicals. They showed that mixtures were more powerful at producing vitellogenin than any of the individual chemicals alone.
They found that the chemicals tended to bioconcentrate in the flesh of the fish: as time passed, the concentration increased. Even low concentration of a weakly oestrogenic chemical could eventually build up to a level that induced vitellogenin production in male fish.
Sumpter and Jobling then asked whether the oestrogen effects of these chemicals would be limited to one species. After reviewing available literature and conducting a limited number of experiments themselves, they concluded, "Most evidence supports the idea that if a chemical is oestrogenic in one species, it will be in all others".
Sumpter and Jobling then asked what the consequences are for aquatic organisms living in a "sea of oestrogen". The answer, they said, is easy: we do not know. The possible effects are "almost endless", because of the large number of roles played by natural oestrogens. They did pinpoint reproduction as the process mostly likely to be disrupted.
In late 1996, US researchers published studies confirming that up-to-date sewage treatment plants in the US can cause the same effects in fish living downstream.
Scientists examined male carp from five locations in the Mississippi River downstream from the Minneapolis sewage treatment plant, and from a tributary, the Minnesota River, which receives heavy agricultural run-off.
They found that carp living near the Minneapolis sewage treatment plant showed "a pronounced oestrogenic effect", namely the production of vitellogenin and reduced levels of testosterone (male sex hormone). Carp from the pesticide-contaminated Minnesota River had sharply reduced testosterone levels but showed no vitellogenin effect. Carp from the largely unpolluted St Croix River were normal.
The US Geological Survey reported in April that industrial contaminants in many US rivers and lakes seem to be affecting the levels of sex hormones in fish throughout the US. The study was conducted by USGS in collaboration with the National Biological Service and the University of Florida.
The study analysed 647 carp collected from 25 streams (including 11 major rivers) in 13 states and the District of Columbia. The streams were selected to represent environmental settings typical of major regions of the country.
The fish were tested for oestrogen and testosterone in their blood. All fish have both; however, the ratio of the two hormones varies between females and males. The ratio is important.
As Bette Hileman has written in Chemical & Engineering News, "In the developing fetus of both humans and animals, a specific ratio of oestrogen to androgens (male hormones) is necessary for sexual differentiation. If the ratio is perturbed, the offspring may be born with two sets of partially developed sexual organs (intersex) or with a single set that is incomplete or improperly developed."
In addition to testing for the oestrogen/testosterone ratio, USGS also tested carp for organochlorine pesticides and PCBs. Organochlorine pesticides (such as DDT, aldrin and dieldrin) and PCBs are known to affect hormone levels in wildlife.
Furthermore, at sites where fish were captured, USGS took samples of sediments and analysed them for total phenols, phthalates and polycyclic aromatic hydrocarbons (PAHs); all three of these classes of chemicals are known to affect hormones in wildlife.
USGS concluded that its most significant findings included these:
- <~>At half the locations tested, one or more male carp were producing vitellogenin at low levels.
- <~>In both male and female carp, the oestrogen/testosterone ratio was most disturbed by dissolved pesticides in water.
- <~>For both male and female carp, the presence of phenols was associated with reduced levels of both oestrogen and testosterone.
USGS researchers said their study was too crude to determine that specific contaminants were causing specific changes in the sex hormones of fish. However, the agency said the findings were "cause for concern".
The implications are clear: whatever is altering the sex hormones of fish originates on the land, and is caused by human activities. Because oestrogen and testosterone perform many of the same functions in fish, birds, amphibians, reptiles and mammals, there is no reason to believe that humans are exempt from the chemicals that are altering the fish.
One might think — based on common sense and simple prudence — that it would be appropriate to begin controlling hormone-disrupting chemicals. Unfortunately, the US EPA has adopted the position of the Chemical Manufacturers Association (CMA), which is this: merely altering the sex hormones of fish or even humans is not sufficient reason to initiate controls on known hormone-disrupting chemicals. It is up to us (the public) to prove that altering our sex hormones is bad for us.
It will take many decades, perhaps centuries, to gather the necessary evidence to convince the likes of the CMA that an "adverse effect" has occurred: think of the history of tobacco. In the meantime, with EPA's blessing, the chemical industry will continue to do its business in our water.
[From Rachel's Environment & Health Weekly. Like 91×ÔÅÄÂÛ̳ Weekly, Rachel's is a non-profit publication which distributes information without charge on the internet and depends on the generosity of readers to survive. If you are able to help keep this valuable resource in existence, send your contribution to Environmental Research Foundation, PO Box 5036, Annapolis, Maryland 21403-7036, USA. In the United States, donations to ERF are tax deductible.]