Course: BIS 105 Environmental Biology

Unit 9 Learning Module

Examples of hazards

Hazardous Metals

Lead

Lead is a highly toxic substance that affects a number of organs and systems in humans, particularly the nervous system. High levels can cause cognitive impairments, weakness in extremities, miscarriage, and reduced fertility in men. Exposure is typically through contaminated water or food. Some homes may have lead water pipes or fixtures, which can leach lead into water. Older homes may also contain lead paint which creates a problem when it flakes or is sanded, creating a dust that is inhaled. As a result, paint containing lead should never be sanded. Simple test kits can identify if your paint contains lead. The United States banned lead paint in 1977.

Mercury

Mercury poisoning can cause a wide variety of symtoms including pain in the extremities, pink skin discoloration, high blood pressure, memory impairment, and kidney disfunction. The most common route of exposure is through consumption of contaminated fish, although plants and livestock can also be contaminated with mercury. Fluorescent light bulbs and dental amalgam also contain mercury. Mercury is an example of a chemical that bioaccumulates and biomagnifies. About half of the atmospheric mercury comes from natural sources such as volcanoes, while the other half is due to human activity. The largest contributor, about two-thirds of the exposure due to human activity, are coal-burning power plants. The saying "mad as a hatter" comes from hatmakers who used mercury to stiffen felt in their hatmaking process, exposing them to high concentrations of mercury vapor.

Asbestos

Asbestos is a collection of six naturally occurring minerals that can cause serious illnesses such as lung cancer, mesothelioma, and asbestosis. Because these minerals form long thin fibers, they have been widely used for fire resistance and building insulation. Canada was one of the main asbestos producing countries and fought against listing it as a hazardous material, but has recently recognized the risks it poses and has halted mining in September 2012. Russia is the main producer in the world.

The EPA has a website dedicated to informing people of the danger and how to deal with abestos, http://www2.epa.gov/asbestos.

Endocrine disruptors

Endocrine disruptors are chemicals that interfere with the endocrine (hormone) system. Since hormones are critical in a wide variety of cellular functions and regulation in most animals, disruption of this system can have far-reaching impacts. Developmental problems, tumors, birth defects, and reproductive disorders are all potential consequences.

Hormones are released from glands and then other cells in the body respond when the hormone binds to a receptor, similar to a lock and key. Many developmental and reproductive changes occur in response to hormonal signaling. Hormone concentrations are usually very low (parts per billion), so potentially even very low exposures may impact an individual. Moreover, since the body naturally produces hormones, the addition of even a small quantity of hormones or chemicals that mimic hormones from outside the body can disrupt proper functioning.

Theo Colburn was one of the early researchers into endocrine disruptors. She published a book entitled Our Stolen Future that explored the impacts of these chemicals. A wealth of information is addressed at the book's website: http://www.ourstolenfuture.org/

Timing of exposure also plays an important role in endocrine disruption. In a fetus, an incredible amount of development occurs in a short period of time. During this period some substances can have a profound impact that may have little or no impact if an adult was similarly exposed. This prebirth exposure can result in permanent changes.

Typically the concentrations of these chemicals are extremely low and many have speculated they do not cause harm because of this. However, endocrine disruptors may be an exception to the rule, "The dose makes the poison." These chemicals may not exhibit the typical dose-response curve seen in other toxicants where increased doses cause increase effects. This is known as a nonmonotonic response, and may be shaped like an inverted U.

Bisphenol A (BPA)

Bisphenol A is a chemical commonly found in some plastic bottles and containers, linings of metal food and beverage containers, and receipt paper. Since these products are ubiquitous in our modern society, the vast majority of people have detectable levels of BPA. A recent study of pregnant women in the U.S. found BPA in 96% of the women (Woodruff et al., 2011).

BPA is a known endocrine disruptor that mimics estrogen, and numerous studies have found that laboratory animals exposed to low levels of it have elevated rates of diabetes, mammary and prostate cancers, decreased sperm count, reproductive problems, early puberty, obesity, and neurological problems. Early developmental stages appear to be the period of greatest sensitivity to its effects, and some studies have linked prenatal exposure to later physical and neurological difficulties. Regulatory bodies have determined safety levels for humans, but those safety levels are currently being questioned or are under review as a result of new scientific studies. A 2008 study by the Yale School of Medicine demonstrated that adverse neurological effects occur in non-human primates regularly exposed to bisphenol A at levels equal to the United States Environmental Protection Agency's (EPA) maximum safe dose of 50 µg/kg/day. In January 2010, the FDA issued a report indicating that, due to findings of recent studies that used novel approaches in testing for subtle effects, both the National Toxicology Program at the National Institutes of Health as well as the FDA have some level of concern regarding the possible effects of BPA on the brain and behavior of fetuses, infants and younger children. A 2012 study found that the neurological effects of BPA are trans-generational in mice. Genetic expression was found to extend into the fourth generation. The authors stated that they believe that their study is the first to have demonstrated that BPA has trans-generational actions on social behavior and neural expression.

In 2012 the FDA banned the use of BPA in baby bottles and sippy cups, after manufacturers had already voluntarily eliminated its use in those products. However, many scientists feel they did not go far enough, since BPA is not banned from use in cans of infant formula, food, or beverages.

BPA appears to have impacts on a wide range of organisms. A 2009 review of the biological impacts of plasticizers on wildlife published by the Royal Society with a focus on annelids (both aquatic and terrestrial), molluscs, crustaceans, insects, fish and amphibians concluded that BPA has been shown to affect reproduction in all studied animal groups, to impair development in crustaceans and amphibians and to induce genetic aberrations.
A large 2010 study of two rivers in Canada found that areas contaminated with hormone-like chemicals including bisphenol A showed females made up 85 per cent of the population of a certain fish, while females made up only 55 per cent in uncontaminated areas.

In response, the plastics industry have begun promoting "BPA-free" products. These plastics typically substitue BPA with bisphenol S (BPS). According to a 2013 study, BPS shares similar problems to BPA in that it has been found to be an estrogen hormone disruptor even at extremely low levels of exposure. Recent research suggests that endocrine disrupting chemicals may in fact be much more common to many or most plastics than was previously realized. A group of researchers looked at 455 common plastic products and found that 70% tested positive for estrogenic activity. After the products had been washed or microwaved the proportion rose to 95%.

Polychlorinated biphenyls (PCBs)

Polychlorinated biphenyls (PCBs) are a class of chlorinated compounds that were used as industrial coolants and lubricants. General Electric was one of the largest US companies to incorporate PCBs into equipment such as transformers, capacitors, and electric motors. Between 1952 and 1977, the New York GE plant had dumped more than 500,000 pounds of PCB waste into the Hudson River.

Exposure to PCBs increases the risk of skin, liver, and brain cancers. The detrimental health effects of PCB exposure to humans became undeniable when two separate incidents of contaminated cooking oil poisoned thousands of residents in Japan (Yushō disease, 1968) and Taiwan (Yu-cheng disease, 1979), leading to a worldwide ban on PCB use in 1977. Recent studies show the endocrine interference of certain PCBs is toxic to the liver and thyroid, increases childhood obesity in children exposed prenatally, and may increase the risk of developing diabetes.

Polybrominated diphenyl ethers (PBDEs)

PBDEs are a class of compounds found in flame retardants that are used in products such as the plastic cases of televisions and computers, electronics, carpets, lighting, bedding, clothing, car components, and foam cushions. They have a similar structure to PBCs and have many of the same health concerns. PBDEs have the potential to disrupt thyroid hormone balance and contribute to a variety of neurological and developmental deficits, including low intelligence and learning disabilities. Many of the most common PBDE's were banned in the European Union in 2006. Studies with rodents have suggested that even brief exposure to PBDEs can cause developmental and behavior problems in juvenile rodents and exposure interferes with proper thyroid hormone regulation.

The Chicago Tribune recently did an investigative series on flame retardants - http://media.apps.chicagotribune.com/flames/index.html.

Phthalates

Phthalates are a group of chemicals most often used to soften PVC plastics which are commonly used in children's toys, medical equipment, and flooring. They can also be found in cosmetics, air fresheners and perfumes. One of the most widely used phthalates is DEHP. An FDA report states, "Exposure to DEHP has produced a range of adverse effects in laboratory animals, but of greatest concern are effects on the development of the male reproductive system and production of normal sperm in young animals. In view of the available animal data, precautions should be taken to limit the exposure of the developing male to DEHP."

In 2009, the Consumer Product Safety Improvement Act (CPSIA) was signed into law by President Bush. It made it illegal to sell children's toys in the United States that contain more than 0.1% of several common phthalates (DEHP, DBP, BBP, DINP, DIDP, and DOP).