Effect of organic amendments on microbial biomass of a tropical soil treated with some herbicides

Studies were carried out on the impact of organic amendments on microflora of soils treated with 2,4- dichlorophenoxy-acetic acid, atrazine, atrazine + metolachlor and paraquat herbicides applied at one and half doses of the recommended rates. Poultry manure-0.05%, urea-0.1 M and glucose–0.1 M of herbicide-treated soils resulted in significant (

An evaluation of the effect of four herbicides on some aquatic organisms

Studies were carried out on the effect of four commonly used herbicides (2,4-D atrazine, atrazine + metolachlor and paraquat) on some aquatic organisms in simulated aquatic ecosystem at 100 ppm, 150 ppm and 200 ppm of the herbicides active ingredients (ai). The effects of the herbicides on pH, blue-green alga – Aphanocapsa sp, aquatic weed –Lemna sp, tadpole (Bufo regularis) and bacterial species were investigated. While 2,4-D resulted in significant decreases in pH value; paraquat resulted in significant increases (p < 0.05). Atrazine and atrazine + metolachlor treatments impacted the most on the lysis of Aphanocapsa sp as all the cells were lysed at 2 days after application. Paraquat treatments at all concentrations resulted in the death of all (20) tadpoles at 2 days after application. Complete tadpole death in atrazine + metolachlor was observed at 8 days after application at 150 ppm and at 12 days after application at 100 ppm. A general decrease in bacterial counts relative to concentrations and days of treatment was observed with paraquat impacting the most on decreases in bacterial counts. Bacterial species isolated from untreated water samples (control) included- Proteus sp, Enterobacter aerogenes, E. coli, Bacillus sp, Pseudomanas sp, Citrobacter sp, Staphylococcus aureus and Flavobacterium sp; while Bacillus (41.2%) and Pseudomonas (56.3%) species were the most frequently isolated bacteria from herbicide treated water samples after 14 days of treatment. Conclusively, herbicides from agricultural run-offs can impair the normal balance of the flora and fauna of the aquatic ecosystem.Keywords: Herbicides, aquatic ecosystem, pH, bacteri

Effect of two commonly used herbicides on soil microflora at two different concentrations

The effect of two commonly used herbicides (atrazine and atrazine + metolachlor) on non-target soil microflora was investigated over a period of 8 weeks. One kilogram soil samples each from maize farm were treated with the herbicides separately at company recommended and one and half (X1.5) recommended rates. Effects of the herbicides on soil pH and percentage organic matter were also investigated. Significant changes in soil pH and percentage organic matter were observed only in atrazine treated soils (P < 0.05). Herbicide treatments at both recommended and X1.5 recommended rates resulted in decreases in microbial counts. Higher concentrations of herbicides treatments resulted in much lower microbial counts compared to soils treated with recommended herbicide does. Herbicide treatments also resulted in the elimination of some microbial species. Pseudomonas sp. and Bacillus sp. were the most frequently isolated bacteria from herbicide treated soils. While A. niger, A. Flavus, Penicillium sp and Trichoderma sp were the most frequently isolated fungi from herbicide treated soils.Keywords: herbicides, microflora, atrazine, metolachor, concentration

Relationship between bacterial density and chemical composition of a tropical sewage oxidation pond

Studies were carried out to examine the performance of the sewage oxidation pond situated in and serving the community of the Obafemi Awolowo University, Ile-Ife, Nigeria. A survey of the coliform and total bacterial populations was carried out. The sewage was also examined for biochemical oxygen demand, dissolved oxygen content as well as for nitrate, phosphate, silica and chloride contents. The mean coliform bacteria counts decreased gradually from 69.1×105 per 100 ml to about 10.1×105 per 100 ml as the sewage moved through the oxidation pond into the receiving stream. A similar decrease in mean biochemical oxygen demand of the sewage from 397.8 Ib/acre/day to 64.2 Ib/acre/day was also observed. The concentrations of nitrate, phosphate and chloride decreased from the pond influent to the pond effluent. On the other hand, both the silica and dissolved oxygen content of the sewage gradually increased from 14.1 to 19.0 mg/l and 8.1 to 13.9 mg/l respectively, across the pond to the effluent. The coliform and total bacterial counts as well as the concentrations of most of the chemicals in the receiving stream increased after being joined by the sewage oxidation pond effluent. It is therefore concluded that the receiving stream was subject to both bacteriological and chemical pollution. Building of additional oxidation ponds or addition of a primary sewage treatment to the existing system is recommended for more efficient wastewater treatment.Key words: Bacterial density, chemical composition, oxidation pond, sewage, tropics