This is particularly true with toxicants in the presence of an adsorptive substrate such as
chitin. For all toxicants presented, with the exception of Kepone, residence time in
aquatic and marine environments was reduced. As shown with 1,2 DCE, toxicants, upon
adsorption to a chitinous surface, select for those microorganisms which are non-sensitive
and, perhaps, pre-adapted for toxicant biotransformation.
The removal of competing heterotrophic microorganisms by the toxicant facilitates rapid
colonization of the chitinous surface by the remaining epiphytic population and may
induce subsequent cooxidative or cometabolic phenomena. Furthermore, this chitin/toxicant interaction may be more pronounced in saline microenvironments than in fresh
water, particularly where readily available energy substrates are abundant.
The organochlorine, Kepone, failed to appreciably degrade in both freshwater and saline
microcosms despite chitin amendment. Subsequent microcosm tests confirmed the
adsorption of Kepone to chitin and selection of non-sensitive strains on these surfaces.
However, microbial degradation by the selected population was minimal. Thus, an
additional factor in toxicant biotransformation is evident, namely the contribution of
functional groups, i.e. chlorine, attached to a parent molecule structure. Despite toxicant
adsorption/ concentration and epiphytic population selection, toxicant biotransformation also is determined by enzyme orientation to the toxicant molecule stoichiometry.
CONCLUSION
Microcosm approaches have been used to develop a correlated interpretative analysis of
fate and effect of a variety of toxicants in aquatic environments. Fate estimates for
important toxic chemical classes such as organophosphates, organochlorines, phenolics
and dichloroethanes may be biased when the availability and influence of naturallyoccurring substrates such as chitin, within the aquatic/marine environment, are not
considered. A more complete discussion on this point is presented in Portier and Meyers,
1984. Thus, examination of changes to the epiphytic microbial community can serve as a
basis for modeling the environmental fate of a toxicant in a dynamic estuarine system as
well as forming the basis of interpreting the impact of the compound on primary trophic
levels in estuarine food webs.
ACKNOWLEDGEMENTS
Portions of the work reported in this paper were funded from grant NA81AA-D-0046, NOAA, Office of Sea
Grant Development. Additional support was obtained from a research and development program funded by the
Louisiana Board of Regents, Contract No. B22.
DAVAR P. and J.P. WIGHTMAN., 1981. Interaction of pesticides with chitosan. Adsorption from Aqueous
Solutions. Plenum Press, pp. 163-177.
GAMBRELL R., 1982. Effect of oxidation-reduction conditions on pesticide persistence. In Determination of the
Environmental Impact of Several Toxicants in Agriculturally Affected Wetlands. pp. 1-44.
HOOD M.A., 1973. Chitin degration in the salt marsh environment. Ph.D Dissertation, Louisiana State
University, Baton Rouge, 158 pp.
HSU S.C. and J.L. LOCKWOOD, 1975. Powdered chitin agar as a selective medium for enumeration of actinomycetes in water and soil. Appl. Microbiology 29: 422-426.
586
chitin. For all toxicants presented, with the exception of Kepone, residence time in
aquatic and marine environments was reduced. As shown with 1,2 DCE, toxicants, upon
adsorption to a chitinous surface, select for those microorganisms which are non-sensitive
and, perhaps, pre-adapted for toxicant biotransformation.
The removal of competing heterotrophic microorganisms by the toxicant facilitates rapid
colonization of the chitinous surface by the remaining epiphytic population and may
induce subsequent cooxidative or cometabolic phenomena. Furthermore, this chitin/toxicant interaction may be more pronounced in saline microenvironments than in fresh
water, particularly where readily available energy substrates are abundant.
The organochlorine, Kepone, failed to appreciably degrade in both freshwater and saline
microcosms despite chitin amendment. Subsequent microcosm tests confirmed the
adsorption of Kepone to chitin and selection of non-sensitive strains on these surfaces.
However, microbial degradation by the selected population was minimal. Thus, an
additional factor in toxicant biotransformation is evident, namely the contribution of
functional groups, i.e. chlorine, attached to a parent molecule structure. Despite toxicant
adsorption/ concentration and epiphytic population selection, toxicant biotransformation also is determined by enzyme orientation to the toxicant molecule stoichiometry.
CONCLUSION
Microcosm approaches have been used to develop a correlated interpretative analysis of
fate and effect of a variety of toxicants in aquatic environments. Fate estimates for
important toxic chemical classes such as organophosphates, organochlorines, phenolics
and dichloroethanes may be biased when the availability and influence of naturallyoccurring substrates such as chitin, within the aquatic/marine environment, are not
considered. A more complete discussion on this point is presented in Portier and Meyers,
1984. Thus, examination of changes to the epiphytic microbial community can serve as a
basis for modeling the environmental fate of a toxicant in a dynamic estuarine system as
well as forming the basis of interpreting the impact of the compound on primary trophic
levels in estuarine food webs.
ACKNOWLEDGEMENTS
Portions of the work reported in this paper were funded from grant NA81AA-D-0046, NOAA, Office of Sea
Grant Development. Additional support was obtained from a research and development program funded by the
Louisiana Board of Regents, Contract No. B22.
DAVAR P. and J.P. WIGHTMAN., 1981. Interaction of pesticides with chitosan. Adsorption from Aqueous
Solutions. Plenum Press, pp. 163-177.
GAMBRELL R., 1982. Effect of oxidation-reduction conditions on pesticide persistence. In Determination of the
Environmental Impact of Several Toxicants in Agriculturally Affected Wetlands. pp. 1-44.
HOOD M.A., 1973. Chitin degration in the salt marsh environment. Ph.D Dissertation, Louisiana State
University, Baton Rouge, 158 pp.
HSU S.C. and J.L. LOCKWOOD, 1975. Powdered chitin agar as a selective medium for enumeration of actinomycetes in water and soil. Appl. Microbiology 29: 422-426.
586