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Chlorothalonil : its environmental fate, toxicology and metabolism in fish


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Davies, PE 1984 , 'Chlorothalonil : its environmental fate, toxicology and metabolism in fish', PhD thesis, University of Tasmania.

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The toxicology of a widely used fungicide, chlorothalonil (TCIN),
was investigated in three species of native Australian galaxiid fish
and rainbow trout, Salmo gairdneri Rich., after measuring environmental
levels in two aerially sprayed north-eastern Tasmanian catchment streams.
TCIN residues (0 - 5 ug/l) were detected intermittently in stream waters
after spraying events. LC50 values determined in flow through tests were
from 12 - 21 ug/l. Investigation of sublethal effects showed short term
anaemia, haemolysis and long-term gill damage quantified by morphometric
analysis. No anaerobic glycolysis was measurable on short-term lethal
exposure, despite a synergistic effect of low oxygen levels measured in
an LC50 test at 50% saturation. A device counting opercular rhythms by
Fast Fourier Transform analysis was designed and tested in conjunction
with experiments to determine respiratory rate and responses of S.
gairdneri to low TCIN levels. A distinct respiratory response was
measured, characterized by elevated ventilation rates, with a threshold
of 20 ug/1 during 2 h exposure. Environmental degradation of TCIN was
studied in stream waters with a variety of substrates, temperatures and
water types. TCIN was found to be a non-persistent pollutant whose
disappearance rates were markedly enhanced by the presence of algal
substrate and the presence of fish. Sediment partition coefficients were
established. In a stream-dosing study, TCIN was found to be highly
associated with suspended sediment.
In order to study metabolism of chlorothalonil (TCIN) in more
detail, a synthetic route was designed and used successfully to produce
(2 14-CN) TCIN. Tracing experiments were carried out in 10 ug/1 exposed
rainbow trout. Significant levels built up in all organs. Protein binding
occurred in the liver. The primary concentration of label occurred in the
gall bladder (up to 4000 ug/g in 96h). Sephadex filtration and TLC showed
that glutathione conjugates were the primary metabolites. Structural
studies were carried out using synthesized model compounds, and the
structures of TCIN glutathione conjugates were fully elucidated by
spectral methods.
Catalysis of the conjugation reaction by hepatic glutathione S-transferase
(GST) enzymes was studied in detail in the three Galaxias species, S. gairdneri and S. trutta. Molecular weights, comparative
activities to another substrate (CDNB), pH optima, induction by TCIN
exposure, binding and inhibition, reaction order, and organ specificity
were all studied. All species were found to have two GST enzymes of
different molecular weight with peak activity toward the two substrates,
14-TCIN and CDNB. Galaxias GST's were consistently lower in molecular
weight than those of the salmonids, indicating a major phylogenetic
difference in this enzyme group. Induction and binding of metallo-thioneins
by TCIN and co-induction with Zn exposure were also studied.
Hepatic GST activity was promoted in S. gairdneri, G. maculatus and
G. truttaceus exposed to low levels of TCIN over four days, and the
response was dose dependent. Confirmation of detoxication by glutathione
(GSH) depletion was obtained by measuring GSH levels in livers of exposed
fish. Despite in vitro inhibition at low GAPDH levels, GAPDH inhibition
was prevented by the presence of glutathione and was low in hepatic
cytosol preparations of similar low GAPDH levels. Inhibition of GAPDH in
livers of TCIN exposed fish was also studied, and found to be only
transitorily affected by exposure to lethal levels.
No similar work on either toxicology, degradation or metabolism of
pesticides in Australia has been reported in the literature. Apart from
same heavy metal and hydrocarbon toxicology studies, almost no such work
has been performed in Australia, most information being derivative from
overseas. This study shows that the toxicological response of the
galaxiids appears to be as sensitive as that of rainbow trout. A case
is made for aquatic toxicological information applied within Australia
to be directly related to information on native and not overseas species.
A proposal is made to screen native fish, both marine and
freshwater, before time-consuming, expensive toxicity tests, possibly
detrimental to native species populations, are carried out. The screening
process involves selecting species "at risk" to classes of pollutants by
studying levels and activities of detoxication enzyme systems. This
proposed procedure is illustrated with the example of a correlation
between GST and GSH levels in Salmo gairdneri, Galaxias auratus, and
Galaxias maculatus, and the LC50 values for TCIN for these species,
determined in this work.
A paper on the synthesis of C 14-TCIN has been accepted for publication.
The manuscript is contained in Appendix 5. Six other papers
have been submitted for publication on the toxicology and metabolism
of chlorothalonil in fish.

Item Type: Thesis - PhD
Authors/Creators:Davies, PE
Keywords: Fungicides, Chlorothalonil, Freshwater fishes
Copyright Holders: The Author
Copyright Information:

Copyright 1984 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
would be pleased to hear from the copyright owner(s).

Additional Information:

Bibliography: leaves 252 - 298. Thesis (Ph. D.) - University of Tasmania, 1984

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