Mutagenic Properties of Pesticides Kimberly Champine

Pesticide Usage Pesticide use by farmers in southeast Missouri provides many opportunities for pesticide contamination of ground water. The ideal outcome of pesticide use occurs when it accomplishes its purpose then breaks down into harmless components such as CO 2 and H 2 O. The breakdown of various pesticide chemicals varies with time and can be affected by factors such as persistence, formulation or soil characteristics.

Groundwater Contamination Groundwater is the water that that lies below the soil surface and fills the pore spaces in and around rock, sand, gravel and other materials. Groundwater moves through water saturated zones called aquifers. The upper level of the aquifer is the water table and fluctuates throughout the year. Contamination occurs when unwanted substances move into the saturated zone.

Classification and Examples of Pesticides

Parathion Parathion is an organophosphate compound and is one of the most toxic insecticides registered with the EPA. Is is a broad spectrum insecticide, nematocide, acaricide, and fumigant. Parathion is used on alfalfa, barley, corn, cotton, soybeans and wheat.

Aldicarb Aldicarb is a member of the carbamate class of chemicals. It is a toxic, systemic insecticide used to control mites, nematodes, and aphids. It is applied directly to the soil and is used on cotton, peanut, and soybean crops.

Atrazine Atrazine is a member of the triazine class of chemicals. It is a broad-leaf pre- emergence herbicide commonly applied to agricultural fields containing corn, apples and grapes. Eighty million pounds of atrazine are applied annually to soils in the US.

Testing Contaminated Ground Water for Mutagenesis Using the Ames Test

Ames Test Used to evaluate the mutagenicity of chemicals Assay is based on the reversion of mutations in the histidine (His) operon in the bacterium Salmonella typhimurium Mutations are changes in the DNA sequence of a gene

Salmonella typhimurium The His operon encodes enzymes required for the biosynthesis of the amino acid histidine Strains with mutations in the His operon are unable to grow without added histidine Revertants that restore His + phenotype will grow without added histidine

Step 1 – Inoculating Plates Spread 0.05 ml (1 drop) of mutant strain of Salmonella to the surface of Minimal Media without Histidine

Step 2 – Apply Groundwater  Add a sterile paper disk to the center of the plate  Apply 0.1 ml of Groundwater, or other suspected mutagen, to the center of the disk  Only cells that are mutated a second time will be able to synthesize Histidine and be able to grow

Typical Results  The larger white disk in the middle is impregnated with the mutagen  The smaller dots are colonies of revertant bacteria.  The more growth indicates a stronger mutagen  Various strains can be used to test for different types of mutations

Interpreting Results Revertant bacterial growth around a disc impregnated with contaminated ground water could indicate possible carcinogenic affects in human beings. The more colonies observed, the higher degree of health risk in the water sample.

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