Pesticide Residues in Aquatic Invertebrates - Pesticides: Evaluation of Environmental Pollution - page 327

deactivated by the oxon metabolite. This results in overstimulation of the peripheral and
central nervous systems (Buchwalter et al. 2004).
Many of the OPPs are used to target insects, and therefore, they may have greater impacts
on nontarget organisms in the class Insecta. Chironomus riparius larvae were exposed in
vitro during the second to fourth instar. The first sign of toxicity was knockdown in all lar-
vae. Tremors were monitored after 1 h of exposure. No movement or response to physical
stimuli was observed. At high concentrations, AChE assays exposed that homogenates from
C. riparius larvae were refractory to chlorpyrifos; in opposition, chlorpyrifos-oxon in a con-
centration-dependent manner inhibited homogenates from C. riparius larvae (Buchwalter
et al. 2004).
OPs are also toxic to aquatic organisms in the subphylum Crustacea. Chlorpyrifos
is highly toxic to Daphnia magna juveniles, 24-h LC 50 is 1.28 nM, and it is more toxic to
Daphnia than malathion and CM (Moore et al. 1998; Kikuchi et al. 2000). In the case of
freshwater shrimp, there was decreased survival of juvenile Caridina laevis , at 24- and 96-h
LC 50 when exposed to diazinon at 0.76 and 0.59 μg/L, respectively (Sucahyo et al. 2008).
The question is why. Organisms have a tendency to be more sensitive to pesticides in the
younger stages. This may be due to younger organisms having a greater surface area to
volume ratio, and their metabolic capacity may be different (Kefford et al. 2004; Sucahyo
et al. 2008).
11.2.3.3 Effect of Carbamate Pesticides on Arthropods
Carbamate pesticides are known to inhibit type “B” esterases, including cholinesterase
and carboxylesterase, by binding to the active site and phosphorylating the enzyme.
However, the action in aquatic organisms is less clear, such as how the transfer of oxygen
occurs (Barata et al. 2004). Carbofuran is the most toxic carbamate pesticide. Carbofuran
derivatives, N- nitroso, and its toxic metabolites (3-hydroxycarbofuran and 3-ketocarbo-
furan) increased the likelihood of mutagenicity in Salmonella typhimurium strains TA98
and TA100 (Nelson et al. 1981). Carbofuran has been linked to cytochrome P450 activities
in organisms (Ray and Ghosh 2006) and has been monitored in insects since the 1960s
(Snyder 2000). Furthermore, Carbaryl affected the predator-prey interactions within a
zooplankton community (Chang et al. 2005).
Many CMs are highly toxic to the class Insecta. Furadan is the commercial name of
carbofuran, which is used to control insects in rice fields in Senegal (Mullié et al. 1991).
Carbofuran is hazardous to fish and invertebrates (Eisler 1985). Acute toxicity of carbo-
furan was studied in Senegal rice fields in 1985. The study found that carbofuran may be
highly toxic to aquatic fauna in rice fields. Additionally, the number of aquatic macroin-
sects was significantly reduced after carbofuran exposure (Mullié et al. 1991).
CMs can have deleterious effects on organisms in the subphylum Crustacea. CMs have
the potential to change the dominant species in aquatic ecosystems. Low concentrations of
carbaryl influenced Daphnia spp.; moreover, Daphnia was the most sensitive organism to car-
baryl (Hanazato 1998). The acute toxicity of carbofuran was monitored in freshwater shrimp
Caridina laevis . The study found the 24-h LC 50 to be 1.70 mg/L. and 0.95 mg/L. for the 96-h
LC 50 (Sucahyo et al. 2008). Daphnia magna , which is widely used to test toxicity, were exposed
to carbofuran to assess acetylcholinesterase (AchE) and carboxylesterase (CbE) inhibi-
tion. The LC 50 of carbofuran on D. magna was 762.93 nM (Barata et al. 2004). Additionally,
Dobsikova (2003) reported a 24-h LC 50 and 48-h LC 50 of 0.0447 and 0.0187 mg/L, respectively,
in D. Magna .