The genotixic potential of commonly used seed protectants

Abstract

The use of agrochemicals has generally increased worldwide due to escalating world population growth and subsequent demand for food. A wide range of agrochemicals has been shown to induce matagenic, carcinogenic and even teratogenic effects. Residues of such chemicals and their by-products can easily find their way into human food. A large proportion of human population is likely to be at risk. This study was undertaken to investigate the genotoxic effects of the grain protectants Lindane (Hexachlorocyclohexane), Actellic (Primiphos Methyl) and Malathion (Dimethyl phosphodithioate). While data on the metabolic toxicity to these grain protectants is available, genotoxic data on the same is scarce. We investigated the potential to induce chromosome aberrations using the Vicia faba root system and the mouse bone marrow system. In the V. faba assay intact lateral roots were exposed to the chemicals dissolved, in 1/150 Sorensens buffer (pH 6), for 1 hour at 22oC  1oC at concentration levels 104, 103, 102, 101, 1, 10-1, 10-2, 10-3, 10-4 ppm. The seedlings were then recovered for 26 hours in Hoaglands solutions. The root tips were then squashed in Feulgen and scored. All the 3 protectants were potent mitotic inhibitors. Anaphase bridges, C-metaphases and fragments were scored in Lindane (concentration ranges 1, 10-1, 10-2, 10-3, 10-4 ppm). Actellic (Concentration ranges 104, 103, 102, 101, 1, 10-1ppm). These effects were dose/rate dependent. In an effort to determine the factors involved in the induction of the aberrations. The following manipulations were conducted. Mitostasis usually implies the inhibition or interference of DNA replication V. faba seedlings were treated with 10-2 ppm MgCl2 for one hour followed by treatment with the protectant. The results obtained showed a significant decrease in the inhibition of mitosis. Mitostasis may also occur because of the depletion of precursors of DNA synthesis i.e. the nucleotides. To test for this, the V. faba lateral roots were treated for 1 hour with nucleotides, followed by treatment with the chemical. The results showed that there was a significant reduction in mitostasis. Variations in pH and temperature during treatment have also been shown to influence the rate of induction of chromosome aberrations. Lateral roots were treated with Sorensens buffer at a range of pH's. i.e. 2, 4, 6, 10 and 12, for 1 hour, followed by treatment with the threshold concentration of the chemical for 1 hour. The results in an increase in the induction of aberrations. A quantity of remants of the grain protectants is likely to be left on the grains after washing. Such are therefore cooked and consumed together with the grain. Chemical metabolites induced by cooking of the grain protectants would most likely be produced, which are likely to have different effects on the V. faba root cells. An attempt was made to investigate this by beilling the chemicals for 1 hour. The results on how a high increase in the induction of anaphase bridges and C-metaphases, in comparison to the controls by all the three grain protectants.

The ability of the 3-grain protectants to induce mutations in yeast Saccharomyces cerevisiae was also determined. Strain rad1-1 was used to test for the induction of gene conversion and reversion mutations and strain D61.M for the induction of chromosome loss. The results indicate that all the grain protectants induced all these effects.

Incurable chromosome aberrations based on genetic diseases are widespread. In view of this, the results call for stringent measures in the handling of these chemicals. "Safer" and/or alternative agrochemicals e.g. by use of biological control.