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The natural breakdown of three pesticides on the UK Red List (dieldrin, simazine and trifluralin) in water and soil varied with environmental conditions. In both sterile and unsterile water, trifluralin was degraded to some extent at 20 and 30°C. In contrast, dieldrin and simazine were stable over the 42 days incubation period. A gradient HPLC method was developed for the simultaneous quantification of the three pesticides in soil. In field capacity soil mixtures of the three pesticides (5 and 10 ppm) showed a similar stability with limited degradation at 20°C but increased rates of degradation at 30°C. At the higher concentration the pesticides naturally degraded at a slower rate. Simazine and trifluralin degradation was significantly enhanced with increasing temperature from 20 to 30°C. Water potential (field capacity~ -0.065 MPa~ and - 0.28 MPa) had little effect on the natural breakdown rate of dieldrin. Simazine showed a greater breakdown in the mid-wetness soil~ while trifluralin was degraded rapidly in the field capacity soil, but not at all in the driest treatment over the 70 day experimental period. In vitro studies on solid agar media overlayed with cellophane showed that of four fungi examined~ Trametes cingulata, Trametes socotrana (tropical species) and Phanerochaete chrysosporium and Polystictus versicolor (temperate species) all except P.chrysosporium were able to grow in the presence of 5 ppm of any of the three pesticides at 20 and 30°C, with the latter only growing at 30°C. At 10 ppm concentration P. chrysosporium did not grow, regardless of temperature or time of incubation (up to 56 days). HPLC was used to quantify the temporal rates of degradation in the solid agar media and this showed that P. versicolor and T. socotrana were very effective at breaking down the three pesticides, at 20 and 30°C. The chosen fungi were grown on chopped straw as a carrier and incorporated into soil microcosms in the ratio of 1:10 containing mixtures of the three pesticides (5, 10 ppm) at 20 and 30°C, and subsequently under different water potential regimes at 20°C only, over periods of 70 days. P. versicolor alone significantly increased breakdown of 5 ppm dieldrin by 26% over untreated controls, while simazine breakdown was increased by 16%. However, for simazine at 30°C there was no difference between temporal rates of natural breakdown and those containing fungal inocula, regardless of concentration. With 5 ppm trifluralin, a maximum breakdown in untreated soil was 67% after 70 days. By contras~ this pesticide was undetectable after 28 days in the presence of the inoculant P . versicolor. This increased to 42 days where a mixture of the two fungi were used. Generally the mixture of fungi used in this study were not as effective in bioremediation of these pesticides as a single species. Field capacity soil appeared to be the best condition for P. versicolor to degrade dieldrin and trifluralin added at 10 ppm. However, for simazine this occurred in the driest water potential (-0.28 MPa) used.

This study involved the investigation of a contaminated soil problem in Gateshead, UK. The site was previously a dumping area from industrial activities for over a hundred years and generated problems of high sulphate concentration and heavy metals in both the soil and the leachate which discharges into the River Tyne. The combination of such contaminants has not been widely investigated in the area of contaminated soil. The study was therefore divided into 2 parts, namely bioremediation of the contaminated soil and leachate treatment by reverse osmosis. The bioremediation study involved treatability tests which included slurry, microbial growth and column tests. The reverse osmosis study involved membrane fouling and leachate pre-treatment experiments. The bioremediation study stimulated the indigenous microorganisms by the addition of nutrients and carbon sources. The soil slurry and microbial growth tests determined the combination of nitrogen and phosphorus required to produce higher C02 evolution as an assessment of microbial activity. It was found in the column tests that the addition of a carbon source and appiopriate nutrient combinations resulted in a significant reduction of sulphate in both the leachate and the soil matrix. Furthermore, this was also accompanied by an increase in the microbial population in the soil matrix. It was also considered that- assimilatory sulphate reduction by microorganisms had taken place since H2S production could not be detected in the open system of the column. However, the high pH of the soil that was higher than 8 possibly caused H2S production undetected in this study. Zinc, manganesea nd copper,i n contrastw ere not reducedi n the soil matrix. Only arsenic showed significant reduction in the soil columns. Heavy metals were precipitateda nd were still presenti n high concentrationsin the leachatea nd would require further treatmenti n the liquid phase.T his was demonstratedb y the study of the use of a LPROM (Low PressureR everseO smosisM embrane)t o treat leachate from the contaminated soil. The reverse osmosis study showed that zinc and arsenic could be reduced by up to 86% and 97% respectively. Sulphate was also satisfactorily reduced up to 99%. However, the study on membrane fouling confirmed that the sulphate concentration was the main effect of fouling. Ferric chloride, aluminium sulphate, barium chloride and polyelectrolyte Zetag 92 were used for coagulation-flocculation in the pretreatment of the leachate. The study revealed that the sulphate concentration could only be reduced at the most by 43% using a FeC13, BaC12 and Zetag 92 combination. FeC13 showed better floc characteristics than alum whereas BaC12 improved sulphate removal but increased the turbidity in the supernatants. However, the use of BaC12 would significantly increase the cost of pretreatment. The study recommended a further investigation into the use of a range of readily available carbon, nitrogen and phosphorous sources in the soil column or at pilot-scale for designing a full-scale bioremediation system. Meanwhile, an investigation into other leachate pretreatment methods such as continuous microfiltration or anti-scalant addition was also suggested.

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No description available.