Environmental Engineering Reference
In-Depth Information
6.1 Introduction
The majority of pesticides exhibit limited stability in the environment and in plants
and animals; it is an extremely important property of these compounds, which, on
theonehand,determinestheeficiencyoftheiraction,and,ontheother,permitsthe
safeuseofagriculturalproductsbyhumans.Thefateofpesticidesinthesoildepends
on the chemical transformations in which the living organisms participate (biotic,
biochemical transformations) and on the physical, chemical, and photochemical
processes. Biotic transformations catalyzed by the enzymes of soil microorganisms
predominate. The highest ability of eficient degradation of pesticides is exhibited
by bacteria, Actinomycetes, and mushrooms. The contribution of mushrooms is the
greatest, reaching even up to 80%. There are at least two causes of this high activity
of soil mushrooms: greater resistance to unfavorable vegetation conditions in com-
parison to bacteria (mushrooms exhibit high liveliness in acidic environment, even
at pH<5) and greater ability of degradation of pesticides by mushroom enzymes.
Soilmicroorganismsexhibitinghighestactivityindegradationofpesticidescomprise
bacteria from the species Arthrobacter , Bacillus , Corynebacterium , Flavobacterium , and
Pseudomonas ; Actinomycetes of the Nocardia and Streptomyces species; and mushrooms
ofthe Penicillium, Aspergillus, Fusarium, and Trichoderma species.
Photochemicaltransformationofpesticidesisrestrictedtosoilandplantsurfacesand
onlytocompoundssensitivetosolarradiation(intherange290-450nm).Itresultsinthe
formation of radicals, which are highly reactive, owing to the presence of a single elec-
tron,whichleads,forexample,inaqueoussolutions,tonumerousreactionsofbreakingof
bondsaswellastorecombinationreactions.
In this chapter, the readers will ind essential information concerning the causes and
transformations of pesticides from various chemical groups and their degradation and
fragmentationintheenvironment.
6.2 The Concept of Degradation and Fragmentation of Pesticides
Manyenvironmentalfateprocesses,includingsorption,hydrolysis,volatilization,trans-
port, and accumulation of bound residues, are coupled with degradation; each of these
processesmayresponddifferentlytoenvironmentalconditions,thusmakingthecompre-
hensionoffactorscontrollingdegradationchallenging.Theimportanceoftheseprocesses
hasbeenrecognizedrecently,leadingtostudiesinwhichseveralkeyfateprocesseswere
investigatedinthesameexperimentsystem.
6.3 Factors Influencing Residual Characteristics
Thecontinuallygrowingamountofinformationonthebehaviorofpesticidesinsoil,and
intheenvironmentingeneral,hasadvancedourunderstandingofthesephenomena.For
thisreason,theparameterizationandtestingofincreasinglysophisticatedmathematical
 
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