BIODEGRADATION OF HERBICIDE ATRAZINE USING SOME SELECTED SOIL BACTERIAL SPECIES

Abstract

The effect of atrazine was significant at P<0.001 level of confidence on soil organic carbon, organic matter, pH, potassium, bulk density, particle density, percentage moisture, available phosphorus, and percentage nitrogen. However, it did not affect soil particle size distribution (sand, silt, and clay), magnesium, porosity, sodium, and manganese. The soils of both the study sites were sandy loam with high amounts of sand. Bacterial species isolated at the forest and garden sites had Pseudomonas aeruginosa, Pseudomonas putida, Bacillus subtilis, Bacillus sphaericus, Staphylococcus aureus, Klebsiella, Escherichia coli, Azotobacter nigricans, Flavobacterium aquaticum, Micrococcus loteus, Salmonella typhimurium, and Proteus vulgaris. Atrazine had an effect on the total heterotrophic bacterial count THBC and the effect was dependent on the concentration of the herbicide, as the lower 3kg/ha, concentrations generally showed higher peak values than the higher concentration 6kg/ha, for both the study sites. Control soils in the forest had the highest THBC. Atrazine was utilized by all the bacterial isolates at different optical density values. A.nigrican had OD 2.1 at day
14th, OD 0.26 at day 21st and OD 0.28 Pseudomonas aeruginosa had OD 0.2 and Azotobacter nigrican had OD 0.03 after 7 days of incubation. There was a decrease in the amount of herbicide detected and an increase in the percentage of biodegradation as the
period of treatment decreased. Lower concentration of 3kg/ha. (300 ppm) atrazine in forest soil had a retention time of 5.61, peak of area of 164, residues detected 287ppm and percentage biodegradation of (4.18 %), while garden soil treated with the same concentration had a retention time of 5.63, area of peak 400, residue detected 296.46ppm and percentage biodegradation (4.85 %) all at the first day of soil treatment. The laboratory studies on the in vitro biodegradation had percentage biodegradation increases with increase in number of days of incubation. Sterilized soil was generally observed to have the lowest degradation rate when compared with the unsterilized. Amongst bacterial isolates, Pseudomonas aeruginosa had the highest percentage of biodegradation followed by P. putida.