Environmental Engineering Reference
In-Depth Information
3.7.2
Maneb and Zineb
Ethyleneurea (EU), ethylenethiourea (ETU), ethylene (bis)isothiocyanatesul-
fide (EBIS), and glycine were formed in irradiated solutions of EBDCs as well
as in the dark. Their structures are shown in Fig. 8. EU is the main decompos-
ition product of photolysis. The time when approximately half of the starting
material is degraded is 10.5 h for the irradiated sample and 23.5 hforthe
non-irradiated sample [89].
Since EBDCs are transformed rapidly to ETU in the aqueous environment
there is a need for information regarding the photolytic fate of ETU. In wa-
ter,ETUisrelativelystabletohydrolysisandphotolysisinaqueousmedia.
Gruiskshan and Jarrow [86] showed that aqueous solutions of ETU exposed
to UV light (above 285 nm) undergo very slow photolysis. Irradiation at an
intensity of 1900
Wcm -2
µ
for 24 hhaveaninsignificantloss( < 5%). Irradi-
Wcm -2 for 15 days resulted in 33% loss of ETU [90]. However,
photosensitized oxidation is considered a major degradation pathway for
ETU [90] in the presence of photosensitizers occurring in natural waters (i.e.,
riboflavin, chlorophyll). For example, the photosensitized oxidation of ETU
using riboflavin leads to concentration less than 5% of that in the dark con-
trol within 4 days [91]. Generally, the photolysis half-life of ETU in natural
water is reported as 1-4 days [90]. ETU is probably oxidized to EU by pho-
tochemically produced hydroxyl radicals. The identified degradates (Fig. 9)
were glycine, 3-(2-imidazolin-2-yl)-2-imidazolidinethione (Jaffe's base), EU,
and hydantoin (2,4-imidazolidinedione) [90].
ation at 3300
µ
Fig. 8 Principal photodegradation products of maneb and zineb in aqueous environ-
ment [89]
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