chapter 03

Chemicals in the environment can accumulate in living tissue by bioaccumulation and biomagnification and become toxic.
- • Bioaccumulation
  Substances that are fat-soluble can accumulate in the fat tissue of an animal over time.
  A stable chemical such as DDT can build up in living tissue to concentrations much greater than that of the environment.
- • Biomagnification
  Fat-soluble chemicals such as DDT becomes increasingly magnified in animals higher on the food chain.
  Consuming large predatory fish such as tuna and swordfish exposes humans to higher toxin concentrations than consumption of smaller fish.
  Review:
- • The insecticide DDT became widely used in the U.S. after WW II to eradicate insects in the mistaken belief that flies caused Poliomyelitis.
  This chemical accumulates in animal fat, and becomes increasingly concentrated in animals high on the food chain.
  DDT was banned in the U.S. in 1972, adhering to a precautionary principle: "better safe than sorry".
The chemical BPA may mimic steroid hormones and act as an endocrine disruptor.
- •
  1. Hormones such as estrogen (or a mimic such as BPA) work by binding to specific cells.
  2. The hormone can enter the nucleus of the cell and bind to the DNA.
  3. This binding may activate or inactivate genes in the DNA.
  4. In turn, this affects the production of proteins encoded by the gene.
  5. The protein can have various effects on the cell's function.
  Thus BPA is a endocrine disruptor, upsetting the delicate balance of cellular processes that are regulated by hormones.
Research by in-vivo and in-vitro experiments as well as epidemiological studies on BPA indicated possible toxicity of the chemical.
- • An in-vivo study involves experimenting with whole, living organisms.
  Male mice whose mothers were fed BPA showed significant increase in size of their prostate glands.
  This correlation suggests that BPA may act as an endocrine disruptor in mice.
- • An in-vitro study involves experimenting with cells and tissues taken from living organisms, typically in petri dishes, test tubes, and flasks.
  Rat brain cells treated with BPA exhibited slower rates of migration across the petri dish they were grown on.
  This indicates possible inhibition of brain development in living organisms.
- • An Epidemiological study involves interviewing subjects about their health conditions to find correlations between disease and chemicals such as BPA.
  This Epidemiological study suggests a correlation between high urine BPA concentrations and diabetes and cardiovascular diseases.
  On the other hand, BPA does not seem to pose a risk for stroke and liver disease; beware of cherry picking of data.