annual report annual report annual report annual report 2005

44
RADIATION CHEMISTRY AND PHYSICS, RADIATION TECHNOLOGIES
Table 1. The experimentally evaluated yield of radiolytic decomposition of MCPA in aqueous solutions of initial concentration
100 mg/l gamma-irradiated with a dose of 1 kGy.
and wastes are being investigated in numerous research
groups in various countries. The objects of
recent studies in this field are mainly organic compounds
of anthropogenic origin, whose presence
in natural waters and wastes is a significant environmental
threat. In experimental laboratory studies,
mostly gamma irradiation from cobalt sources is
employed and the papers published in the last year
deal with radiolytic degradation of numerous aromatic
compounds such as p-chlorophenol [1], catechol
[2], dihalobenzenes [3], p-nonylphenols [4],
2,3-dihydroxynaphthalene [5], benzophenone [6]
and 2-chloroanisole [7]. The conditions of radiolytic
decompositions have been also optimized for polycyclic
aromatic hydrocarbons benzo[a]pyrene [8]
and fluoranthene [9]. The electron beam (EB) irradiation
was employed for radiolytic degradation
of nonylphenol ethoxylates, carboxylates and nonylphenols
[10], 2-chlorobiphenyl [11], and also for
several metal ions from industrial wastes [12]. The
decomposition of dyes has been reported with the
use of EB in the presence of hydrogen peroxide
[13], while methylene blue radiolysis with gamma
radiation, protons and helium ions [14].
Several papers published recently have been
devoted to radiolysis of pesticides. Gamma radiolysis
was reported for herbicide 2,4-dichlorophenoxyacetic
acid (2,4-D) [15,16] and acetochlor [17].
The published results of our work dealt with EB
degradation of herbicide dicamba [18].
The subject of the present studies is another
chlorophenoxy pesticide – 4-chloro-2-methylphenoxyacetic
acid (MCPA) Generally, chlorophenoxy
herbicides, which have potential toxicity towards
humans and animals, are suspected mutagenes and
carcinogens, and are used worldwide on a large
scale as plant growth regulator for agricultural and
non-agricultural purposes. Among them, MCPA
is used in amounts exceeding 2000 tons per year in
West European countries. In the literature on degradation
or removal of MCPA for environmental
purposes mostly photodegradation methods have
been reported. In our earlier studies on the decomposition
of this pesticide with gamma radiation it
Fig.1. Comparison of experimental data with kinetic modeling for the yield of degradation of (A) MCPA of initial
concentration 0.5 mM in aerated solutions of different pH, and (B) formation and decomposition of CMP in
irradiated solutions of MCPA. Data for pH 1.5 – experimental (•) and calculated (), data for pH 7.0 – experimental
(•) and calculated (◦), data for pH 11.5 – experimental () and calculated ().