Eagles and Valentine's Day - the DDT Connection

Allow me to attempt a tour de force and link the subject of the last blog entry, bald eagles, with the holiday on everyone’s mind this month (whether you want to admit it or not), Valentine’s Day.

DDT is the Link
The 1950s were blessed with a wonderful new chemical called DDT (Dichloro-Diphenyl-Trichloroethane), which killed every insect known to man, and hence could be used in a myriad of industries from agriculture to head lice treatments. Unfortunately, like everything that seems too good to be true, DDT turns out to be… well, let me put it to you this way: its use is now completely banned in North America. The red flags were first noticed when the number of bald eagles started dwindling in the United States. Pretty soon, the link was explained: DDT causes thinning of eggshells, and hence lost eagle clutches. The eagle population was nearly decimated, but luckily the problem was caught in time, DDT banned, and eagles are now rebounding.

DDT Affects Sexual Behaviour, Too!
But wait – DDT had other interesting effects on animal development and behaviour. It turns out that DDT is mistaken for estrogen (the “female sex hormone”) by the body of many animals. On a strongly DDT-contaminated site in California, male gulls developed oviducts (typically a female reproductive organ). Many males also failed to engage in reproductive behaviour, and the scarcity of reproductively competent males meant females had few males to help them rear their young. As any single-parent will tell you, it is difficult to do it all on your own. To solve this conundrum, some female-female pairs arose to care for the young, the so-called “lesbian gulls”. (Ref.: Fry & Toone, 1981). If you think that’s unexpected, check out this BBC article about a similar environmental pollutant that is transforming polar bears into hermaphroditic mammals (having both male and female sex organs!).

Your Woes?
DDT takes a long time to decay in the environment, and while it has been banned since 1972 in the United States, it can still be detected in most of our bodies (yes, YOUR body too – In fact, 4 prominent Canadian politicians were recently tested for pollutants in their bodies and found to be “contaminated” (link to the CTV report HERE). DDT is thought to affect the reproductive behaviour of many amphibian, reptile, bird, and mammal populations, but the big question on everyone’s mind is: Is it affecting OUR sexual development and behaviour?

Are Men Becoming Extinct?
In the recent movie Children of Men, the human species has become infertile, leading to hopelessness and the collapse of civilization. Is this science-fiction or a preview of things to come (yikes!)? The incidence of cryptorchidism in human males (a condition where the testes fail to drop after birth – a vital development since the testes need to be at a slightly lower temperature than the body to ensure the sperms’ survival) appears to be on the rise, more than doubling since the 1950s (Ref.: Carlsen et al., 1992). Testicular cancer has tripled in the last 50 years (Ref.: Giwercman & Skakkebaek, 1992). Sperm count also appears to be declining across the board in all human populations (Ref.: Carlsen et al., 1992). Whether the environmental estrogen mimics are causing these alarming trends is a matter of some debate, but it is one that needs to be resolved soon!

Of Eagles of Men
DDT almost wiped out eagles from the face of this planet, and it is possible that the same thing is happening to us now. More studies are required, but evidence is accumulating that environmental pollutants affect sexual behaviour in many animal species. Humans are part of this biosphere – we cannot escape it. So this Valentine’s Day, as you celebrate the fact that your sexual behaviours are still intact, take a moment to ponder that every chocolate you eat may contain traces of DDT…and may be altering the behaviour you will display in future Valentine’s Day…