By Peter Montague
A lengthy new report from the US National Institute of Environmental Health Sciences [NIEHS] describes serious deterioration of the male reproductive system in many regions of the world and suggests it may be caused by environmental chemicals that interfere with hormones.*
The report begins by describing negative trends in men's reproductive health, then describes similar findings among wildlife, and finally reviews evidence that certain chemicals could cause the observed problems. Here is part of the summary provided by the authors of the new study:
"Male reproductive health has deteriorated in many countries during the last few decades. In the 1990s, declining semen quality has been reported from Belgium, Denmark, France, and Great Britain. The incidence of testicular cancer has increased during the same time. Incidences of hypospadias [a birth defect of the penis] and cryptorchidism [undescended testicles] also appear to be increasing. Similar reproductive problems occur in many wildlife species. There are marked geographic differences in the prevalence of male reproductive disorders. While the reasons for these differences are currently unknown, both clinical and laboratory research suggest that the adverse changes may be interrelated and have a common origin in fetal life or childhood."
The authors say they strongly suspect that the common origin is exposure to environmental chemicals (pesticides, plastics, detergents and others) that interfere with hormones.
The authors emphasise that chemicals that interfere with hormones may not be the only cause of the recent decline in male reproductive health. Other chemicals may poison men by a mechanism that does not involve hormones. "For example", they say, "some chemicals that are now known as occupational toxicants were shown to affect the semen quality of the workers through a toxic action on the gonads, without any apparent estrogenic effects." Oestrogen is the main female sex hormone.
The authors review recent studies showing declining sperm quantity and quality among men in many countries, and a few studies that show no such declines. In general, they see declines in urban areas and no declines in rural areas. Rural France and Finland, in particular, seem not to be experiencing a sperm decline.
Worldwide impact
Still, the authors summarise the situation as "decreasing sperm quality worldwide", and they see an urgent need for understanding the causes: "Follow-up of semen quality is very important, since the sperm concentration has decreased drastically during the last two generations and the declining trend appears to be continuing".
In testicular cancer, too, there are geographical differences. Increases are apparent in the US, England and Wales, Scotland, the Nordic and Baltic countries, Australia and New Zealand. Finland seems to be an exception. The authors suggest that good, steady sperm quality and the low testicular cancer rate in Finland, a mostly rural country, may be somehow linked. Within countries there are differences: whites in the US are three times as susceptible to testicular cancer as are African-Americans.
"... it is obvious that there is a worldwide trend toward an increased incidence of testicular cancer ...", the authors of the report conclude.
"Other disorders of the male reproductive tract may also be increasing in incidence, with several European countries reporting a progressive rise in hypospadias ... and an apparently emerging trend toward an increasing incidence of testicular maldescent."
Wildlife
Similarly, male reproductive problems can be observed among wildlife. Gastropods (periwinkles and whelks), best known for the sea shells they live inside, worldwide have shown sex reversal because of exposure to a compound of the metal tin. Tributyltin, widely used in paint to keep seaweed and barnacles from growing on the bottoms of boats and ships, is now known to change male gastropods into female gastropods.
Alligators and turtles have had their sex lives disrupted by exposure to pesticides in Florida and in laboratory experiments. The sex of turtles is normally determined by the temperature at which their eggs incubate. However, eggs incubated at male-producing temperatures but painted with PCBs produce female turtles instead.
PCBs are industrial chemicals, banned in the US in 1976, but still found everywhere in the environment. The same PCB-induced sex reversal can be seen in alligator eggs. Furthermore, male alligators in pesticide-contaminated lakes in Florida have such small penises that they are sexually incompetent —a result of exposure to hormone-disrupting pesticides.
Male fish exposed to hormone-disrupting chemicals discharged by sewage treatment plants begin to produce a protein called vitellogenin, which is normally produced only by female fish as a step toward making eggs. In England and Wales male fish produce vitellogenin when they are caged in river waters below sewage treatment plants. The river water has become oestrogenic.
Florida panthers, which get a large dose of hormone-disrupting chemicals by eating raccoons (which get these chemicals from the fish they eat), have undescended testicles, poor sperm production and other reproductive problems.
DES exposure
The NIEHS report reviews the experience of male children whose mothers were exposed to DES, a synthetic sex hormone. Between the late 1940s and the early 1970s, DES was given to 5 million pregnant women to prevent miscarriage and pregnancy complications.
The sons of these women thus became a "natural experiment", offering an opportunity to study the effects of human exposure to hormone-disrupting chemicals in the womb. Here is the authors' summary:
"Exposure to DES during pregnancy results in increased risk for several male reproductive disorders, such as cryptorchidism, urethral abnormalities, epididymal cysts [cysts in the sperm reservoir of the testicle], and testicular hypoplasia [small testicles]. In addition, the semen quality of DES sons is worse than that of controls. Incidence of testicular cancer is approximately doubled among DES sons compared to the general population, but whether this represents a true increase of the cancer risk is equivocal."
In sum, the authors say, "Reproduction is a major concern because disturbances of this process rapidly threaten populations as a whole. The male reproductive system is very sensitive to the influence of an excess of estrogen; therefore, estrogenlike effects in the environment are a primary suspect for causing the increased reproductive disorders of men and wildlife animals."
Dramatic changes
And: "Male reproductive health has received remarkably little attention considering that subfertility affects 5% or more of men and that prostatic hypertrophy [enlargement of the prostate gland] or cancer is a major problem for older men. It is now evident that several aspects of male reproductive health have changed dramatically for the worse over the past 30 to 50 years ...
"While the etiologies [causes] underlying these apparent changes are currently unclear, both clinical [i.e., human] and laboratory [i.e., animal] research suggests that all of the described changes in male reproductive health appear interrelated and may have a common origin in fetal life or childhood. This means that the increase in some of the disorders seen today originated 20 to 40 years ago, and the prevalence of such defects in male babies born today will not become manifest for another 20 to 40 years or more.
"Trends in the reproductive health of species other than man also raise the possibility of environmental factors as partial etiologic contributions in a decline noted in male reproductive health of wildlife."
In sum, "Taken together, this growing body of evidence suggests that environmental factors that resemble female sex hormones may be having an adverse effect on the reproductive capacity and well being of diverse species."
From, Rachel's Environment & Health Weekly.]
* Jorma Toppari and others, "Male Reproductive Health and Environmental Xenoestrogens", Environmental Health Perspectives Vol. 104 Supplement 4 (August 1996), pp. 741-803. This new report is a revised and abridged version of a report originally commissioned by the Danish Environmental Protection Agency in Copenhagen.