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Biomedical subjects

C M Tu

Publications and source records attributed to C M Tu.

At least 19 recordsLinked to original sources
PubMed1993

Effect of fungicides, captafol and chlorothalonil, on microbial and enzymatic activities in mineral soil.

Tests were conducted to determine the effects of fungicides, captafol and chlorothalonil, on microbial and enzymatic activities in sandy loam. The results indicated that when captafol or chlorothalonil was added to the sandy loam, bacterial and fungicidal populations initially decreased with the treatments but recovered rapidly to levels similar to those in the controls. No inhibition on oxidation of soil ammonia or organic sulfur was observed. The fungicide treatments significantly increased oxygen consumption from the decomposition of organic matter indigenous to the soil. Both fungicides suppressed invertase and amylase for 1 day. However, the inhibitory effect disappeared after 2 days. Captafol depressed dehydrogenase for 4 days and recovered to equal to that of control after 7 days. No inhibitory effect on urease and phosphatase was shown with the fungicidal treatments. Although some stimulatory influences of fungicides on microbial and enzymatic activities were found in the soil, in no instance were the effects dramatic or sufficient enough to be considered important to soil fertility.

Bacteria↗
PubMed1982

Effect of pyrethroid insecticides on soybean and its pathogen Rhizoctonia solani Kuehn.

Laboratory tests were conducted to determine the phytotoxicity and fungitoxicity of five pyrethroid insecticides; cypermethrin, decamethrin, fenpropanate, fenvalerate and permethrin at different rates to soybean and its pathogen Rhizoctonia solani Kuehn. Fungitoxicities of the chemicals on pathogen were in the order of thiram greater than permethrin greater than cypermethrin greater than decamethrin greater than fenvalerate. Phytotoxicities on soybean seedlings were decamethrin greater than cypermethrin greater than fenpropanate greater than fenvalerate greater than permethrin greater than Arasan. A comparative study on both phytotoxic and fungitoxic effects indicated that the pyrethroids were less effective than Arasan for use in the control of this soil borne plant pathogen.

Fungicides, Industrial↗
PubMed1982

Persistence and mobility of nitrofen (niclofen, TOK) in mineral and organic soils.

Residues of nitrofen in farm soils, persistence of nitrofen in field microplots, mobility of nitrofen in natural soils and the role of microbial flora in its degradation were studied. Muck soils from vegetable farms in southwestern Ontario contained up to 35 ppm nitrofen in mid-season (August), which decreased to 18 ppm by October. The herbicide was less persistent in sand than in muck. Degradation was slightly faster in sand and muck soils receiving two sprays, than in those sprayed once. From an initial deposit of ca. 2 and 10 ppm resp., in sand and muck field microplots, ca. 2 and 15% persisted after 16 wk. Leaching of nitrofen by water through sand was negligible, and it was even more strongly adsorbed onto organic soil. Natural microbial flora seemed to play an important role in the degradation of nitrofen in soil. Ca. 15 and 38% resp., of the initial concentration persisted in natural sandy loam and muck 16 wk after treatment at 10 ppm, whereas about 94 and 82% resp., persisted in sterilized sandy loam and muck at the same period.

Herbicides↗
PubMed1981

Effects of pesticides on activities of enzymes and microorganisms in a clay soil.

Laboratory experiments were conducted to determine the effect of 32 pesticides applied at 2 levels on populations of microorganisms, activities of urease, dehydrogenase, phosphatase and nitrogenase in a clay loam incubated for 1 week. Results indicated that a decrease in bacterial number was observed with thiram for 2 days and stimulation with chlorpyrifos after 7 days. Some fungicides and fumigants inhibited fungal numbers for 2 days. The recovery was rapid and stimulatory effects on microbial numbers were evident in many samples. None of the pesticides inhibited soil urease drastically. Formazan formation was not suppressed vigorously by the treatments. With the exception of DD and Vorlex at a high level, none of the treatments inhibited phosphatase in the hydrolysis of p-nitrophenyl disodium orthophosphate. A temporary decrease in nitrogenase activity in acetylene (C2H2) reduction was observed with many pesticides. The low amount of pesticides applied to the clay loam is unlikely to have detrimental effects on soil microbes and the enzymes important to soil fertility.

Acetylene↗
PubMed1981

A laboratory study of the persistence of carbofuran and its 3-hydroxy- and 3 keto-metabolites in sterile and natural mineral and organic soils.

In a laboratory study, the persistence of carbofuran and its 3-hydroxy- and 3-keto-metabolites was examined separately over 16 wk in sterile and natural organic (muck) and mineral (loam) soils. Carbofuran was relatively persistent in sterile soils; at 8 wk 77% remained in the sterile muck and about 50% remained in the sterile loam. In the natural muck 25% of initial carbofuran remained at wk whereas in the natural loam carbofuran had completely disappeared by that time. The 3-ketocarbofuran was very short-lived even in the sterile muck where only 50% remained at 1 wk. The 3-hydroxycarbofuran degraded appreciably on zero day in the natural soils (with conversion to 3-keto-carbofuran) and about 90% had disappeared in 1 wk. A more detailed study of the persistence of 3-hydroxycarbofuran in the natural soils showed complete disappearance in 2 days in loam and in 3 days in muck. The 3-ketocarbofuran produced from the 3-hydroxy-carbofuran reached a maximum concentration in 1 day and then disappeared within 4 days in loam and about 1 wk in muck.

Actinomycetales↗
PubMed1981

Effect of DDT, fauna and flooding on microsomal growth in soil.

Laboratory experiments were conducted to determine the effect of DDT, fauna and flooding on microbial growth in a sandy loam. Results indicated that soil microorganisms can tolerate the presence of DDT. Earthworms singly or in combination with springtails affected the average population of fungi in the DDT-untreated samples and of aerobic bacteria in the DDT-treated soils. Soil animals did not appear to have any effect on the populations of anaerobic bacteria. However, waterlogging brought about a decrease in aerobic bacteria and fungal populations, and an increase in anaerobic bacteria in both soils.

Animals↗
PubMed1979

Influence of pesticides on acetylene reduction and growth of microorganisms in an organic soil.

The effects of 32 pesticides at two concentrations on acetylene reduction (non-symbiotic nitrogen fixation), nitrogen fixers, bacteria and fungi in an organic soil were assessed. None of the pesticide treatments suppressed C2H2 reduction as compared to controls. No significant inhibition of the population of non-symbiotic nitrogen fixers occurred. However, stimulatory effects were observed with treatments of fensulfothion, fonofos, oxamyl, DDR, TeloneR and Telone CR. Bacterial and fungal populations showed temporary declines but all recovered within 7 days to levels similar to or higher than those in the controls.

Acetylene↗
PubMed1978

A screening technique for assessing effects of pesticides on population and activities of non-target soil microorganisms.

A simplified technique for assessing the effect of pesticides on non-target soil microorganisms was developed. Changes in microbial population determined by the dilution plate method, in nitrification by the soil perfusion technique, and in oxygen consumption using a differential respirometer are the only measurements required. A comparison of the effects observed for three pesticides, dieldrin, chlorpyrifos and Vorlex, in three soil types with those produced by an antibiotic, a fungicide, a nitrification inhibitor and steam pasteurization of the soil clearly demonstrate the effectiveness of the simple technique.

Chlorpyrifos↗