Abstract:
The natural breakdown of three pesticides on the UK Red Lis~ 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 contras~ 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.