DEPARTMENT OF ANIMAL AND ENVIRONMENTAL BIOLOGY,

This study evaluated the neurotoxic effects of long-term exposure to N-(1,3-dimethylbutyl)- N′-phenyl-p-phenylenediamine quinone (6PPDQ), a transformation product of the tire additive 6PPD, on the brain of Clarias gariepinus juveniles. The research, motivated by growing concern over tire-derived contaminants, aimed to determine the effects of 6PPDQ on acetylcholinesterase (AChE) activity, acetylcholine (ACh) levels, and brain histology. A total of 237 fish were exposed to 500 µg/L, 1,000 µg/L, and 1,500 µg/L of 6PPDQ for 28 days under laboratory conditions, following OECD sub-lethal toxicity guidelines. AChE activity was determined using Ellman’s spectrophotometric method, while histopathological alterations in the telencephalon and optic tectum were assessed with haematoxylin and eosin (H&E) staining. Results revealed a significant (p < 0.05) dose- and time-dependent inhibition of AChE activity with a corresponding increase in ACh concentration. Histological analysis showed neuronal shrinkage, vacuolation, pyknosis, and mild gliosis in exposed fish, indicating oxidative stress and neuroinflammatory responses. The study concludes that prolonged exposure to 6PPDQ disrupts cholinergic neurotransmission and alters brain histoarchitecture in C. gariepinus. These findings highlight the ecological risks of tire-derived pollutants and emphasize the need for environmental monitoring and stricter regulation to mitigate their impact on aquatic life and ecosystem health.

The use of pest control techniques in Agriculture have proven to be highly effective in addressing food insecurity and agricultural production issues. This study was conducted to compare growth and evaluate the yield of sweet potato under three different pest control techniques in relation to exposure to insect herbivory.These pest control techniques include physical exclusion, chemical exclusion and those without exclusion (no control). Sweet potato plants excluded physically were completely screened from herbivory using a net house, those excluded chemically were sprayed weekly with 0.01% Lambda-cyhalothrin and those without exclusion were fully exposed to herbivory. Stem length, number of leaves, number of runners, percentage herbivory and number of damaged leaves were parameters used to compare growth while tuber count, heaviest tuber and average tuber weight were used to evaluate yield. Sweet potatoes physically excluded significantly (p < 0.05) gave highest growth rates and this was evidently seen in their stem length, number of leaves and runners. Plants subjected to chemical exclusion and those without exclusion statistically had higher mean values in terms of yield than those physically excluded. However, the difference in yield from the three treatments did not vary significantly (p > 0.05) in tuber count (H2 = 2.34, p > 0.05), heaviest tuber (F2 = 1.67, p > 0.05) and average tuber weight (H2 = 4.24, p > 0.05). Sweet potatoes allocate more resources on growth when completely screened off from insect herbivory as seen by those physically excluded but this is was not enough to warrant improved yield.