05 - Heavy Metal: Effects of Environmental Toxins on C. elegans
trace nutrients can become toxic at higher doses. Other heavy metals such as mercury and lead have no known biological benefits but can cause long-lasting and irreversible biological damage. Exposures to heavy metals are a common and dangerous environmental health issue. The fast metabolic rates and limited self-repair abilities of nerve cells, as well as the large number of chemical messengers used in interneuron communication, make the nervous system par- ticularly vulnerable to these chemicals. This is especially true for the still-developing nervous systems of children and infants. Regardless of age, damage to the nervous system can affect everything from learning to motor coordination to the regulation of internal systems like circu- lation and digestion (Table 1). While some of these effects can be observed immediately after exposure, others take months or even years to manifest. Because it is often difficult to detect early symptoms of exposure and because damages to the nervous system can be permanent, health strategies related to heavy metal neurotoxicity focus on prevention through the early identification and removal. C. elegans have a similar nervous system to humans and are susceptible to most heavy metals. Mercury, copper, lead, chromium, nickel, cadmium, aluminum, cobalt, zinc, and manganese have all been observed to have a negative effect on the wild-type strain. While toxicology studies have traditionally focused on lethal doses or lethal concentrations (LC), advances in chemical detection technologies have led to a growing interest in the effects of smaller, and often more environmentally relevant concentrations, as well as the synergistic effects of two or more chemicals. In this experiment, you will be investigating the effects of low-level heavy metal exposure on both wild-type and adr-2 mutant C. elegans . Each strain will be exposed to a potentially damag- ing chemical for four minutes. (Copper Sulfate, Cadmium Chloride, and Zinc Sulfate are pro - vided but you or your teacher may bring in additional solutions to test.) You will observe and count the thrash rate of a single worm at the beginning, middle, and end of this time period. In addition, you will carry out controls where both strains are exposed to a non-harmful buffer so - lution for four minutes and again observe and calculate the start, middle, and end thrash rates. Results can be graphed and shared with other lab groups.
TABLE 1: Symptoms of Heavy Metal Neurotoxicity
• Uncontrollable obsessive and/or compulsive behavior • Sexual dysfunction • Chronic Fatigue • Attention Deficit Disorder • Predisposition to Alzheimer’s Disease, Multiple Sclerosis, Parkinson’s Disease
• Headache • Loss of Vision • Imbalance
• Loss of Circulation • Flu-like symptoms • Tingling, Weakness or Paralysis of the Limbs • Loss of memory and cognitive function • Depression
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