DETERMINATION OF PESTICIDE RESIDUES IN SOME VEGETABLES AND HEAVY METALS IN THE VEGETABLES AND SOILS FROM SELECTED FARMLANDS IN MINNA, NIGERIA
DETERMINATION OF PESTICIDE RESIDUES IN SOME VEGETABLES AND HEAVY METALS IN THE VEGETABLES AND SOILS FROM SELECTED FARMLANDS IN MINNA, NIGERIA
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Date
2016-08
Authors
ABDULHAMID, Zulaihat
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Abstract
The aim of this study was to assess the level of pesticide residues and heavy metals in three staple vegetables commonly cultivated in Minna and also determine the physico-chemical properties and heavy metal content of the farm soils where the vegetables were grown. Amaranthus hybridus (spinach), Hibiscus esculentus (okra), Telfairia occidentalis (fluted pumpkin) and soil samples were collected from seven selected farms in Minna, Niger State. The vegetables were analysed for the presence of six pesticides (cypermethrin, carbofuran, lambda-cyhalothrin, aldrin, endrin and heptachlor) using gas chromatography triple quadrupole mass spectrometry and six heavy metals (cadmium, copper, iron, manganese, nickel and zinc) by atomic absorption spectrometry. The soil samples of the farms were also assessed for the heavy metals and physico-chemical properties that include pH, electrical conductivity, particle size, organic carbon, organic matter, exchangeable bases and cation exchange capacity. The soil-plant transfer factors between the level of heavy metals in the soils and their levels in the vegetables were also determined. The transfer factor results revealed no absorption of Cd in the three vegetables of all farms except in Keteren gwari farm. The TFs values for Zn and Cu from Mandela farm were the highest for all vegetables compared to other farms. The results of the pesticide residues analysis revealed that none of the okra and fluted pumpkin leaves showed the presence of any of the pesticides analysed while spinach samples from farms in Chanchaga and Mandela areas contained cypermethrin in the range of 0.60-8.65 mg/kg.
Heptachlor was also detected in the spinach samples of the same farms during full scan but their levels were below the detection of the instrument used. The results for the physicochemical properties of the farm soils indicate: pH; 5.77-7.70, soil organic matter 1.63-3.87 %, electrical conductivity; 17-37 μS/cm. The particle size results was: sand; 65.00-95.80, silt; 1.60-33.60, clay; 0.60-6.00 and exchangeable bases: Na+; 0.48-1.64, K+; 0.05-
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0.45, Mg2+; 0.11-0.31, Ca2+; 2.30-4.21, cation exchange capacity; 3.68 to 4.85. The mean levels of heavy metals in the soil samples were found to be in the range: Cd (0.18-1.34 mg/kg), Cu (6.71-47.59 mg/kg), Fe (1942.13-2205.90 mg/kg), Mn (182.48-371.78 mg/kg), Ni (0.65-6.90 mg/kg), Zn (15.70-225.20 mg/kg). The result of the vegetables analysed showed that Amaranthus hybridus contained: Cd (4.65-4.85 mg/kg); Cu (4.31-30.17 mg/kg); Fe (27.06-683.95 mg/kg); Mn (13.01-81.00 mg/kg); Ni (1.22-1.44 mg/kg); Zn (2.48-164.78 mg/kg), while Hibiscus esculentus contained: Cu (11.22-19.90 mg/kg); Fe (114.71-189.86 mg/kg); Mn (33.26-103.61 mg/kg); Ni (1.24-1.54 mg/kg) and Zn (38.81-97.95 mg/kg), Telfairia occidentalis: Cd (5.11-7.16 mg/kg); Cu (4.96-36.93 mg/kg); Fe (116.72-592.28 mg/kg); Mn (95.67 to 572.72 mg/kg); Ni (1.36-3.42 mg/kg); Zn (7.25-69.06 mg/kg). The concentration of the metals in the soil samples varied according to the following trend: Fe>Mn>Zn> Cu>Ni>Cd. The average concentration of all the metals in each farm also gave the trend Farm B>Farm G>Farm E>Farm C>Farm F>Farm D>Farm A. The control farm (A) contained lower levels of most of the investigated metals The findings indicate the presence of heavy metals in all the farm soils but only Fe was above the FAO/WHO standards of 1000mg/kg. The trends of the average concentration of all six metals in the different vegetables from all farms were Spinach: Fe>Zn>Mn>Cu>Cd>Ni; okra: Fe>Zn>Mn>Cu>Ni and fluted pumpkin leaves: Fe>Mn>Zn>Cu>Cd>Ni. The result also revealed spinach was the only vegetable sample in this research that was contaminated with pesticides and heavy metals. This implies that continuous monitoring and education of farmers about proper use of pesticides is necessary. Indiscriminate disposal of waste in the environment and citing farms near dumpsites, garages, road side etc should be discouraged.
Description
A DISSERTATION SUBMITTED TO THE SCHOOL OF POSTGRADUATE STUDIES, AHMADU BELLO UNIVERSITY, ZARIA
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE AWARD
OF THE DEGREE OF
DOCTOR OF PHILOSOPHY (Ph.D) IN ANALYTICAL CHEMISTRY.
DEPARTMENT OF CHEMISTRY,
FACULTY OF SCIENCE
AHMADU BELLO UNIVERSITY, ZARIA
NIGERIA
Keywords
DETERMINATION,, PESTICIDE RESIDUES,, VEGETABLES,, HEAVY METALS,, VEGETABLES,, SOILS,, SELECTED FARMLANDS,, MINNA,, NIGERIA