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Browsing Soil and Land Systems publications by Author "Ahmad, R."
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Item Metadata only Differences in sorption behaviour of carbaryl and phosalone in soils from Australia, Pakistan, and the United Kingdom(C S I R O Publishing, 2001) Ahmad, R.; Kookana, R.; Alston, A.; Bromilow, R.Sorption of 2 nonionic pesticides, carbaryl (1-naphthyl methylcarbamate) and phosalone (S-6-chloro-2,3-dihydro-2-oxobenzoxazol-3-ylmethyl O,O-diethyl phosphorodithioate), was investigated for 48 soils from Australia, Pakistan, and the United Kingdom. A wide variation in sorption affinities of the soils to carbaryl and phosalone was observed. The sorption coefficient (K d) values for carbaryl ranged from 0.19 to 23.0 L/kg in Australian soils, from 0.99 to 59.7 L/kg in Pakistani soils, and from 1.09 to 23.0 L/kg in the UK soils. The K d values for phosalone ranged from 4.8 to 443 L/kg in Australian soils, from 15.5 to 1182 L/kg in Pakistani soils, and from 18.1 to 205 L/kg in the UK soils. To eliminate the effect of variation in organic carbon content among the soils, the K d values were normalised to the fraction of soil organic carbon (K oc ). However, K oc values for both pesticides varied by about an order of magnitude across the soils, decreasing in the following order: Pakistani > Australian > UK soils. Correlation between K d and organic carbon content of the soils was poor (r 2 = 0.44 and 0.46). The particulate organic C (53 µm–2 mm) was only slightly better correlated with K d than the total organic C in the <2 mm fraction of the soils. Thus soil organic C content alone is not a good predictor of sorption even for nonionic pesticides such as carbaryl and phosalone. Caution is needed during extrapolation of overseas data to predict sorption under local conditions.Item Metadata only Sorption of ametryn and imazethapyr in twenty-five soils from Pakistan and Australia(Marcel Dekker Inc, 2001) Ahmad, R.; Kookana, R.; Alston, A.Changes in aerobic bacteria and autotrophic nitrifier numbers, and in respiration and nitrification in two soils treated with cinosulfuron at 42 (field rate) and 4200 μg/kg were studied after 1 and 4 weeks of incubation under laboratory conditions. Only nitrification at 1 week was slightly inhibited by the cinosulfuron treatment, even at the field rate. In vitro toxicity tests carried out in agar media on representative aerobic bacteria, fungi and Azotobacter strains isolated from the two soils, as well as on nine collection soil bacteria, showed that only a very high cinosulfuron concentration (100 mg/l) can have negative effects on the growth of a limited number of soil heterotrophic microorganisms, under conditions similar to those of soil environment. The absence of three branchedchain amino acids increased bacterial sensitivity, thus showing the importance of the chemical conditions and suggesting acetolactate synthase enzyme blockage as the toxicity mechanism. It is concluded that cinosulfuron has a negative effect on only a few aspects of the microbial community in soil ecosystems, even at concentrations higher that those currently in use.Item Metadata only Surfactant-enhanced release of carbaryl and ethion from two long-term contaminated soils(Marcel Dekker Inc, 2004) Ahmad, R.; Kookana, R.; Alston, A.The potential of five nonionic surfactants, Triton X-100, Brij35, Ethylan GE08, Ethylan CD127, and Ethylan CPG660 for enhancing release of carbaryl and ethion from two long-term contaminated soils was evaluated using the batch method. Incorporation of the surfactants into soils enhanced the release of both pesticides to various extents, which could be related to the type of pesticides and type and the amount of surfactants added. Release of ethion was dramatically enhanced by aqueous concentrations of surfactants above their critical micelle concentration values. This was attributed to solubility enhancement through incorporation of the highly hydrophobic compound within surfactant micelles. A concentration of 10 g L-1 of various surfactants released >70% of the total ethion from the soil irrespective of the surfactant. For carbaryl, the surfactants were effective at low concentrations and dependence on concentration was lower than in the case of ethion. The ethylan surfactants (GE08, CD127, and CPG660) had a higher potential than Triton X-100 and Brij35 for releasing the pesticides. However, there was still a significant portion of carbaryl (11% of the total) and ethion (17% of the total) left in the soil. Our study also showed that there must be an optimal concentration of each surfactant to maximize the mass transfer of pesticides. At some threshold concentration level, additional surfactant started to inhibit the mass transfer of solute from the soil into the water. The results suggested that surfactants could help remediation of soils polluted by pesticides. The choice of surfactant should be made based on the properties of pesticides.Item Metadata only Syringe filtration as a source of error in pesticide residue analysis in environmental samples(Springer-Verlag, 2001) Ahmad, R.; Kookana, R.; Alston, A.Item Metadata only The nature of soil organic matter affects sorption of pesticides. 1. Relationships with carbon chemistry as determined by 13C CPMAS NMR spectroscopy(Amer Chemical Soc, 2001) Ahmad, R.; Kookana, R.; Alston, A.; Skjemstad, J.The structural composition of soil organic matter (SOM) was determined in twenty-seven soils with different vegetation from several ecological zones of Australia and Pakistan using solid-state CPMAS 13C NMR. The SOM was characterized using carbon types derived from the NMR spectra. Relationships were determined between Koc (sorption per unit organic C) of carbaryl(1-naphthylmethylcarbamate) and phosalone (S-6-chloro-2,3-dihydro-2-oxobenzoxazol-3-ylmethyl O,O-diethyl phosphorodithioate) and the nature of organic matter in the soils. Substantial variations were revealed in the structural composition of organic matter in the soils studied. The variations in Koc values of the pesticides observed for the soils could be explained only when variations in the aromatic components of SOM were taken into consideration. The highly significant positive correlations of aromaticity of SOM and Koc values of carbaryl and phosalone revealed that the aromatic component of SOM is a good predictor of a soil's ability to bind such nonionic pesticides.