Environmental Engineering Reference
In-Depth Information
Some pesticides such as organochlorines, organophosphates, and carbamates are
known to cause morphological damage to the fish testis. They also affect female fish in
the same way. They cause delayed oocyte development and inhibition of steroid hormone
synthesis.
Experimental exposure of fish to pesticides has shown to depress protein values in the
brain, gills, muscle, kidney, and liver. In the kidney and the liver, there is evidence of sig-
nificant decrease in the protein content due to stress in elimination and also in metabolism
(Tilak et al. 1991).
Organophosphorus pesticides vary in their toxicity to different species. Interference with
endocrine hormones affects reproduction, immune function, development, and neurologi-
cal functions in several species of wild animals. In fish, endocrine disruptors interrupt
normal development and cause male fish to have female characteristics. These outward
symptoms of developmental disruption are accompanied by reduced fertility and even
sterility in adults as well as lower hatching rates and viability of offspring. Many studies
show a direct relationship between concentrations of pesticides and related chemicals in
fish tissues and depressed hormone concentrations. Disruption of the balance of endocrine
hormones during the development of young fish can also cause defects of the skeletal sys-
tem, resulting in deformities and stunted growth (Goodbred 1997). The common pesticide
synergist piperonyl butoxide increases carbaryl toxicity (carbaryl is a neurotoxic carba-
mate pesticide). In fish, acute toxicity of a carbaryl-piperonyl butoxide mixture was over
100 times that of carbaryl alone (Singh and Agarwal 1989). In addition, carbaryl increases
the acute toxicity of the phenoxy herbicide 2,4-D, the insecticides rotenone and dieldrin (an
organochlorine), and the wood preservative pentachlorophenol (Statham and Lech 1975).
Sublethal effects of the organophosphate insecticide phenthoate are also synergized by
carbaryl in fish, resulting in AChE inhibition (Rao and Rao 1989) and both morphological
and behavioral changes (Rao and Rao 1987). While the toxicity of combinations of chemi-
cals is rarely studied, the ability of carbaryl to interact with a large number of chemical
classes is striking.
Polychlorinated pesticides are endocrine-disrupting chemicals (EDCs). They may
be harmful, as they disturb the endocrine system and reproduction in animals and
humans (Fossi et al. 1999; Taylor and Harrison 1999). These changes are most visible
in aquatic animals, as over 100,000 endocrine-active chemicals are discharged directly
into freshwater and marine ecosystems (Trudeau and Tyler 2007). Their presence in the
environment poses a threat to numerous populations and reduces biodiversity (Fossi
et al. 2001).
OCPs have been extensively used for agriculture and vector control purposes in
Tanzania. The pesticides applied on land eventually find their way to the aquatic environ-
ment, thus contaminating it. The pesticides are transported to aquatic bodies by rain run-
off, rivers, and streams and associate with biotic and abiotic macroparticles (Colombo et al.
1990). They are removed from the surface to the benthic layers by settling of the particles
into the water column (Allan 1986). The lipophilic nature, hydrophobicity, and low chemi-
cal and biological degradation rates of OCPs have led to their accumulation in biological
tissues and the subsequent magnification of their concentrations in organisms progressing
up the food chain (Swackhamer and Hites 1988; Vassilopoulou and Georgakopoulous-
Gregoriades 1993). Consumption of biota from a contaminated aquatic body is considered
to be an important route of exposure to persistent OC compounds (Johansen et al. 1996).
Humans, being the final link in the food chain, are mostly affected, and consequently,
the general public has become increasingly concerned about the potential risk to human
health from the consumption of such polluted biota. Furthermore, OCPs in the aquatic
Search WWH ::
Custom Search