Environmental Engineering Reference
In-Depth Information
Flooding suppresses the amount of oxygen present in soil and, as a result, the hydrolysis (i.e.,
decomposition by reaction with water) of carbofuran under fl ooded conditions tends to be chemical, as
opposed to microbial. In fl ooded non-sterile, anaerobic (i.e., absent of oxygen) soil conditions, car-
bofuran is more rapidly hydrolysed but its hydrolysis products (carbofuran phenol and 3-hydroxy
carbofuran) resist further degradation (Venkateswarlu, Siddarame-Gowda and Sethunathan 1977).
The persistence of carbofuran in submerged soils has also been confi rmed in other tropical countries
such as the Philippines and China (Caro, Freeman, Glotfelty et al. 1973; Aquino and Pathak 1976;
Venkateswarlu, Siddarame-Gowda and Sethunathan 1977). A number of enzymes, bacteria and fungi
also facilitate the degradation of carbofuran in soil and aquatic environments (e.g., the microorgan-
ism
Actinomyces
, which is responsible for converting carbofuran to carbon dioxide (McRae 1989).
A number of other microorganisms involved in the process, including
Pseudomonas,
Flavobacterium
,
Achromobacter
,
Arthrobacter
,
Sporocytophaga
and
Corynebacterium
have also
been identifi ed in soils and are discussed elsewhere (e.g., McRae 1989; Lalah, Kaigwara, Getenga
et al. 2001).
Although carbofuran and its metabolites have been detected in soils in Kenya and the degradation
process is well understood, the mechanism/process of metabolism in non-target organisms such as
fi sh, birds and other wildlife species has not yet been formally investigated. The fi ndings discussed
in this section indicate that carbofuran (in the form of its metabolites) is fairly persistent in irriga-
tion systems, which may pose an ongoing exposure threat to aquatic organisms. Given that some
of the metabolites formed from chemical and microbial degradation of carbofuran are highly toxic
(3-hydroxycarbofuran and 3-ketocarbofuran are the two of greatest concern, as outlined in Chapter 1),
a directed investigation of soil and water-dwelling organisms is essential in order to better under-
stand the toxicity of these metabolites within the environment.
3.2.3 General purchase and application of pesticides
Sections 3.2.1 and 3.2.2 discussed the use of pesticides (primarily carbofuran/Furadan) in rice cul-
tivation and the environmental fate of the compound in Kenyan soils and agricultural areas. This
section provides an overview of the distribution and use of pesticides in Kenya. The pesticide indus-
try in this country is composed of a) companies that manufacture the active ingredients used in
pesticide formulations, b) companies that incorporate the active ingredients into the formulations
and c) representatives of manufacturers and/or importers of pesticides and related products not oth-
erwise represented in Kenya (Wandiga, Lalah and Kaigwara 2002). The Pyrethrum Board of Kenya
extracts pyrethrins (i.e., botanical compounds with insecticidal properties) from pyrethrum (a herb
in the
Asteraceae
family). The Kenya Farmers Association (KFA) is involved in the distribution of
pesticides. Most representatives of pesticide manufacture and distribution are overseas-based and
include companies such as Rhone Poulenc, Twiga Chemicals, Murphy Chemicals, Shell Chemical
Industries and British East Africa (BEA) Company.
A great many insecticides/acaricides, herbicides, fungicides, and others not classifi ed (e.g.,
avicides, rodenticides and miticides) are imported into Kenya every year. Approximately 20%
of pesticides are imported in technical form (i.e., as active ingredients) then formulated locally,
while the rest are imported as ready-to-use, formulated products. Most farmers in Kenya buy
pesticides from retail stockists, distributors, or through their cooperative societies and unions.
Financial incentives are sometimes available to farmers, especially to members of the cooperative
societies. Furadan and related carbamate pesticides are marketed through the company Juanco
Ltd. According to the PCPB, Furadan is imported for 'restrictive use' only (i.e., by 'informed'
operators/users). PCPB deems that pesticides classifi ed as 'restricted' are extremely toxic and
should only be handled by trained, experienced and well-equipped operators who are licensed by
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