Chemicals—Friend and Foe?
WE MAKE many decisions in life by weighing advantages against disadvantages. For example, many people buy a car because of the convenience it offers. But against that convenience they have to weigh the cost of owning the car—insurance, registration, depreciation—and of keeping the car roadworthy. They also have to consider the risk of injury or death due to accidents. The situation is much the same with synthetic chemicals—their advantages have to be weighed against their disadvantages. Take as an example the chemical called MTBE (methyl tertiary butyl ether), a fuel additive that enhances combustion and cuts vehicle emissions.
Thanks in part to MTBE, the air in many cities in the United States is the cleanest it has been in years. But cleaner air “has come at a price,” reports New Scientist. This is because MTBE is a potential carcinogen, and it has leaked from tens of thousands of underground gasoline storage tanks, often contaminating groundwater. As a result, one town now has to bring in 82 percent of its water from outside, at a cost of $3.5 million a year! New Scientist says that this disaster “could become one of the US’s most serious groundwater pollution crises for years.”
Some chemicals have been banned and taken off the market altogether because of the damage they cause to the environment and to health. ‘But why,’ you may ask, ‘does this happen? Are not all new chemicals thoroughly tested for toxicity prior to release?’
Problems With Tests for Toxicity
Actually, testing chemicals for toxicity is a blend of science and guesswork. “Risk assessors do not know how to draw a sharp line between ‘safe’ and ‘unsafe’ exposures to any chemical,” says Joseph V. Rodricks in his book Calculated Risks. That is true even of drugs, many of which are produced synthetically. “Even the most careful testing,” says The World Book Encyclopedia, “cannot always reveal the possibility that a drug might produce an unexpected harmful effect.”
Laboratories have certain built-in limitations. They cannot, for example, fully simulate a chemical’s behavior in the diverse and complex outside world. The world outside the laboratory abounds with hundreds, even thousands, of different synthetic chemicals, many of which can interact with one another as well as with living things. Some of these chemicals are innocuous on their own, but if they join together, outside or inside our bodies, they can produce new, toxic compounds. Certain chemicals become toxic, even carcinogenic, only after the body’s metabolism processes them.
How do risk assessors try to determine a chemical’s safety in the light of such challenges? The standard method has been to give laboratory animals a measured dose of the chemical and then try to apply the results to humans. Is this method always reliable?
Are Tests on Animals Reliable?
Besides raising ethical questions regarding cruelty to animals, testing toxins on animals raises other questions. For instance, different animals often react quite differently to chemicals. A small dose of highly toxic dioxin will kill a female guinea pig, but that dose has to be increased 5,000 times to kill a hamster! Even closely related species like rats and mice react differently to many chemicals.
So if the reaction of one animal species is no sure predictor of the reaction of another species, how certain can researchers be that a particular chemical will be safely tolerated by humans? The fact is, they cannot really be certain.
Chemists surely have a difficult task. They have to please the people who want their creations, appease those concerned about animal welfare, and satisfy their own consciences that their products are safe. For these reasons, some laboratories are now experimenting with testing chemicals on human cells in culture. Time will tell, however, if this makes reliable guarantees of safety possible.
When Laboratory Tests Fail
The pesticide DDT, still widely found in the environment, is one example of a chemical that was wrongly declared safe when first released. Scientists later learned that DDT tends to remain in organisms a long time, which is also the case with other potential toxins. What are the tragic consequences of this? Well, the food chain, made up of millions of tiny creatures, then fish, and finally birds, bears, otters, and so on, becomes a living funnel, concentrating toxins in the final consumers. In one case, a population of grebes, a species of water bird, was unable to hatch a single chick for over ten years!
These biological funnels are so efficient that some chemicals, though barely detectable in the water, become concentrated in astounding amounts in the final consumers. Beluga whales in North America’s St. Lawrence River are a good example. They have toxin levels so high that they must be treated as hazardous waste when they die!
Certain chemicals present in many animals have been found to masquerade as hormones. And it is only recently that scientists began to uncover the insidious toxic effect these chemicals can have.
Chemicals That Mimic Hormones
Hormones are important chemical messengers in the body. They travel through our bloodstream to other parts of our body, where they either stimulate or suppress a certain function, such as body growth or reproductive cycles. Interestingly, a recent press release by the World Health Organization (WHO) said that “a rapidly growing body of scientific evidence” indicates that certain synthetic chemicals, when taken into the body, interfere with hormones by either imitating them in a harmful way or blocking them.
The chemicals involved include PCBs,a dioxins, furans, and some pesticides, including DDT residues. Called endocrine disrupters, these chemicals have the potential to disrupt the normal workings of the body’s endocrine system, the source of hormones.
One hormone that these chemicals mimic is the female sex hormone estrogen. A study published in the medical journal Pediatrics suggests that an increased prevalence of early puberty among many girls could be linked to estrogen-containing hair products as well as environmental chemicals that mimic estrogen.
Exposing a male to certain chemicals at a critical time in his development can have adverse effects. “Experiments have shown,” says a report in Discover magazine, “that PCBs applied at just the right time during development can change male turtles and alligators into females or ‘intersex’ individuals.”
In addition, chemical toxins weaken immune systems, leaving animals more prone to viral infections. Indeed, viral infections seem to be spreading farther and faster than ever, especially among animals high on the food chain, such as dolphins and seabirds.
In humans, children are the ones who are affected the most by chemicals that mimic hormones. Children born to women who ingested PCB-contaminated rice oil in Japan some years ago “suffered from physical and mental developmental delays, behavioral problems including hypoactivity and hyperactivity, abnormally small penises, and IQ scores five points below average,” Discover magazine reports. Tests performed on children exposed to a high level of PCBs in the Netherlands and in North America revealed similar adverse effects upon their physical and mental development.
Also linked to these chemicals, reports WHO, may be the increase in “hormonally sensitive” cancers among men and women, such as breast, testicular, and prostate cancer. In addition, in a number of countries, the evidently ongoing decrease in the average sperm count in men, as well as the quality of the sperm, may be linked to the increase in the use of chemicals. In some lands, the average sperm count has almost halved in 50 years!
In the previous article, one doctor was quoted as saying that we are “an experimental generation.” It seems that she is right. True, many of our chemical creations have paid us back well, but others have not. We are wise, therefore, to avoid unnecessary exposure to chemicals that have the potential to hurt us. Surprisingly, many of these can be found in our homes. Our next article will discuss what we can do to protect ourselves from potentially dangerous chemicals.
a PCBs (polychlorinated biphenyls), in widespread use since the 1930’s, are a family of over 200 oily compounds used in lubricants, plastics, electrical insulation, pesticides, dishwashing liquids, and other products. Though PCB production is now banned in many countries, between one and two million tons have been manufactured. Toxic effects have resulted from discarded PCBs that have found their way into the environment.
[Picture on page 7]
These whales are so toxic that they are considered hazardous waste when they die
©George Holton, The National Audubon Society Collection/PR