This research studied the eco-toxicological effects of pesticide residues on soil biological sentinels.
Nitrobacter
and
Nitrosomonas
sp. was isolated from Soil samples gotten from dumpsite in Benin City and cultured
using Winogradsky medium. The bacterial isolate was characterized and identified based on its cultural, morphological
and biochemical characteristics. After 4 to 5 days of growth,
Nitrobacter and
Nitrosomonas Counts obtained from
Winogradsky medium ranged from 1.87±0.95 to 2.43±1.1x10
4cfu/g. The pesticides were observed to have negative
effect on the growth of
Nitrobacter and
Nitrosomas sp. in broth culture media. The effective and lethal concentration
(EC
50) and (LC
50) for each of the pesticides were observed to decrease with increase in the time of exposure and the
effects of the two pesticides on both nitrite oxidations by
Nitrobacter sp. and ammonia oxidation by
Nitrosomonas sp.
were similar. The results also showed that earthworms had weight loss and death at different concentration of the
pesticide and time of exposure, with the lethal concentration (LC
50) of aldrin being 2.84mg/ml while that of lindane
was 3.54mg/ml after 48hr of exposure period. More so, the result obtained from this study suggest that autotrophic
transformation by nitrifying bacteria and earthworm which enhances soil fertility (hence significant in crop production)
may be hindered in an ecosystem polluted with these pesticide formulations, as nitrification processes will be reduced.
Thus, more efforts should be geared at reducing the indiscriminate and illegal use of pesticides (banned or approved).
