Assessing organochlorine pesticide residues in food crops cultivated on soil alluvial plain of some rivers in Ekiti State, Nigeria

ABSTRACT

The use of pesticides in modern agriculture became inevitable owing to improvements in crop protection and yield, whereas their residues in crops and other non-target environmental matrices remain matters of health concern. Therefore, this study is conducted to estimate pesticide contamination in food crops cultivated on floodplains of some rivers in Ekiti State, Southwest Nigeria, and their possible health risk. Soil samples were collected from the farms at 5, 25 and 45 m perpendicular to the river at upper, middle and lower courses of the river while crops sample appropriates were taken randomly from the farms. Samples of soil and food crops taken were subjected to laboratory treatments before they were analysed for organochlorine pesticides using standard procedures. The total soil OCPs range (μg/kg) at Irintan, Omi-Eye and Egbigbu floodplains were 7.50–9.28, 8.72–9.94 and 7.33–9.21, respectively, whereas total crops OCPs range (μg/kg) at Irintan, Omi-Eye and Egbigbu were 21.35–41.75, 12.05–51.89 and 19.42–107.48, respectively. The risk estimate of food crops consumption from the floodplains indicated that there may not be health risk associated with their consumption because the estimated daily intake was relatively lower than the standard reference dose and hazard index was less than one. However, the recent use of banned organochlorine pesticides was given by the ratio of β/α+γ benzene hexachloride residues values, which were greater than 0.5 in soil samples at the studied farms. Consequently, this should be a concern to the international community; this underscores the need for a stricter government regulation in line with United Nations’ safeguard for environment.

INTRODUCTION

Pests and diseases have been known as major factors responsible for the decline in crop production worldwide. The advent of chemical pesticides has, without doubt, greatly improved agricultural production as regards crop production and yield, thus making their use almost inevitable (Oyinloye et al., 2021; Onyeka and Ayibapreye, 2022). To improve agricultural yield, excessive pesticides are used by farmers to control the growth of weeds and to prevent crop damage by insects, rodents and mites (Zonkpoedjre et al., 2023). Aside agriculture, many pesticides such as insecticides, herbicides and fungicides are equally used for household purposes in the form of sprays, powders and liquids for controlling mosquitoes, ticks, cockroaches and bugs. Pesticides have numerous benefits, but the risk aligned with their use is high (Singh et al., 2023). Organochlorine pesticides (OCP) comprise a large group of structurally diverse compounds used to control agricultural pests, plant diseases and vectors of humans in Central Asia, India, China and Africa (Olisah et al., 2020; Jadon and Kumar 2023).

Organochlorine pesticides may have significant short and long-term health effects even at trace concentrations on non-target organisms. Exposure to OCPs has been linked to various health issues. OCPs have been linked to: 1. an increased risk of breast and prostate cancer and lymphoma, 2. reproductive problems in men and women, including decreased fertility and miscarriages, particularly with respect to hexachlorocyclohexane (HCH), and prenatal exposure to α-HCH, β-HCH, ο,p’-dichlorodiphenyldichloroethane (DDD) and p,p’-DDD has been associated with an increased risk for neural tube birth defects, 3. neurological problems, which they are thought to be via bioaccumulation in the body over time, potentially leading to Parkinson’s disease (HCH) and Alzheimer’s disease p,p’-dichlorodiphenyldichloroethylene (DDE), 4. immune system disorders, with dichlorodiphenyltrichloroethane (DDT) causing the dysregulation of interleukin 6 (IL-6), leading to chronic inflammation, and having been related to oxidative stress and immune suppression, thus increasing susceptibility to infections and other diseases, 5. endocrine disruptors that can cause developmental problems in children (DDT) and reproductive problems in adults and 6. low doses of OCPs have been strongly linked to various chronic diseases including diabetes and cardiovascular diseases (Brenna et al., 2015; Cohn et al., 2015; Shan et al., 2015; USEPA-IRIS 2019; Calderon-Garciduenas et al., 2023; Zonkpoedjre et al., 2023).

Based on chemical composition, there are four major types of pesticides: organochlorine, organophosphorus/organophosphate, carbamates and pyrethriods (Yadav and Devi, 2017; Kaur et al., 2019; Shah et al., 2020; Shah et al., 2022). The organochlorine compounds are generally recognised for their low aqueous solubility, low polarity, high lipid solubility, ability to bioaccumulate, long half-life and potential for long-range transport (Jayarat et al., 2016; Joseph et al., 2020; Sosan et al., 2020). These could account for increased organochlorine concentrations along food chain reported by different researchers indicating bioaccumulation and biomagnification in the upper part of the food chain, especially in humans (Chandra et al., 2021). In addition, the half-lives of organochlorine pesticides vary from months to years and in some cases decades (Joseph et al., 2020) and is one of the reasons for classifying them as persistent organic pollutants; thus, there is a ban on their usage by the United Nations (Tzanetou and Karasali, 2022). In Nigeria, the use of OCPs was banned in 2008 by the National Agency for Food and Drug Administration and Control (Tongu et al., 2023). They are, nevertheless, still being used unofficially in large quantities in most developing countries including Nigeria, Ghana, Togo, Benin, Pakistan and Argentina, among many others, owing to their effectiveness as pesticides and their relatively low cost and possibly owing to weak import control and lack of logistics to monitor pesticides (Zonkpoedjre et al., 2023).

Ekiti State is blessed with floodplains, many of which are used for growing arable crops during the dry season period of November–April every year. The floodplains are prone to contaminants including pesticides washed from nearby farms, carried down by flood and deposited on the floodplains at the recession of the flood (Olawale et al., 2017). The crops planted on the floodplains can take up the pollutants, concentrating them in their edible portion at amounts high enough to cause concern to animals and human beings (Hasan et al., 2020). Human exposure to pesticide residues through diet is assumed to be five orders of magnitude higher than other exposure routes such as air and drinking water (Farshad et al., 2020). One of the Sustainable Development Goals (SDGs 3) of United Nations is to promote good health and well being.

A lot of researchers have reported studies conducted on pesticides residues in many developed countries (Tsakiris et al., 2015; Ozcan et al., 2016; Cui et al., 2020; Liu et al., 2023) including reported cases of contamination levels of pesticides in vegetable and maize as well as in food crops (Grewal et al., 2017; Kapeleka et al., 2020; Galani et al., 2021; Ezeani et al., 2022; Alokail et al., 2023; Dinede et al., 2023; Singh et al., 2023). Studies on pesticides contamination in foods in Nigeria have been on food crops grown on dry land, with scanty reports on floodplains, one of which is Aiyesanmi et al., (2021) where the researchers observed high spatial distribution of organochlorine pesticides and a predominance of chlorothalonil, δ-BHC and p,p’-DDT in the studied floodplain soils. However, no reports available are related to OCP on crops grown on floodplain soils in Nigeria. Therefore, the objective of this study is to assess the level of OCP residues in soil and food crops cultivated on some floodplains in Ekiti State, Southwest Nigeria, and thus to estimate their possible potential risk to human health.

MATERIALS AND METHODS

STUDY AREA

Nigeria comprises 36 states, one of which is Ekiti State. The state is located over 250 metres above sea level between longitudes 4° 45’ and 5° 15’ East of Greenwich Meridian and latitudes 7° 15’ and 8° 50’ North of Equator. Ekiti State has two distinct seasons: the wet season, which happens between May and October, and the dry season, which occurs between November and April each year. The state has many hills from which many notable rivers in the Southwestern part of Nigeria take their sources. At the bases of the hills are floodplains that farmers use for dry season farming (Fig. 1).

Fig. 1 Map of Ekiti State displaying the sampling sites (https://www.nigeria)

SAMPLE COLLECTION AND PREPARATION

Three sites were used for the study: Irintan floodplain at Ogbese, Ise-Ekiti (05° 22.04700’E, 07° 30.43200’N, Altitude 420 m); Omi-Eye floodplain at Erio-Ekiti (04° 57.92400’E, 07° 37.30400’N, Altitude 417 m) and Egbigbu floodplain at Ayetoro-Ekiti (05° 09.12400’E°, 07° 55.45700’N, Altitude 531 m). Owing to the fact that the sites were inaccessible during the rainy season, sampling was done between November 2019 and April 2020, which were dry season months during which the floodplains could be accessed. Soil sampling at each farm was done at a depth of 0–30 cm with the aid of a stainless steel auger at distances of 5, 25 and 45 m perpendicular to the course of the river at upper, middle and lower courses of the river channel. Equally, food crops comprising leafy vegetable (Talinum triangulare), pepper (Capsicum annum) and maize (Zea mays) were collected randomly from the farm. All samples were put in separate polythene bags, appropriately labelled and transported to the laboratory under a sealed box. At the laboratory, the soil samples were air dried, disaggregated with agarte mortal and pestle, sieved with 2.0-mm (BS) stainless steel mesh and kept in polyethylene terephthalate (PET) bottles pending analysis (Okoya et al., 2013). The food crop samples were air dried to constant weight, ground and sieved with 2-mm (BS) stainless steel mesh and stored in PET bottles pending the analysis (Ogbonaya et al., 2017).

SAMPLE ANALYSIS

The reagents used were of analytical grade, and glass wares used were cleaned as prescribed by Gakuba et al., (2019). The extraction of organochlorine pesticides in soil and food crops was conducted using the method described by Fasuyi and Oyegoke, (2018). In total, 20 g of each sample and 20 g of sodium hydrogen carbonate were mixed together in a pre-cleaned 250 cm³ conical flask. A 50 cm³ mixture of acetone and n-hexane (1:1 v/v) was mixed with the sample. This was followed by sonication in a high frequency ultrasonic bath for 10–15 minutes. The extract was then decanted into a round bottom flask. The extraction process was repeated with additional 50 cm³ of the acetone and n-hexane mixture, sonicated and allowed to settle before decanting into same round bottom flask. The combined extract was concentrated to 2 cm³ using a rotary evaporator. The extract was redissolved in 5 cm³ n-hexane and later concentrated to 2 cm³ in a rotary evaporator at 40°C.

EXTRACT CLEAN-UP

A 15 cm (length)×1 cm (internal diameter) column plugged at its lower end with glass wool was packed with 5-g activated silica made in slurry form in dichloromethane. In total, 2 g of anhydrous sodium sulfate (Na₂SO₄) was placed on top of the silica gel to absorb water in the sample or solvent in the clean-up extract. Pre-elution was done with 15 cm³ dichloromethane without exposing the sodium sulfate layer to air to prevent the drying up and cracking of the packed silica gel adsorbent. The extract was then introduced into the column and allowed to sink below the sodium sulfate layer. Elution was done three times each with 10 cm³ portions of dichloromethane (DCM). The eluate was evaporated to dryness on a rotary evaporator at about 45°C using a gentle stream of pure nitrogen (99.99%). The dried eluate was reconstituted with 1 cm³ trimethylpentane and transferred into glass GC-MS vials in readiness for instrumental analysis.

GAS CHROMATOGRAPHIC OPERATING CONDITIONS

The OCP in the extracts were determined by a Gas Chromatograph coupled with Electron Capture Detector (GC-ECD) (Yin-Hung et al., 2023). The sample (1 μL) was injected into the injection port of an Agilent 7980 Autosampler GC system equipped with an Electron Capture Detector. The separation was performed on a fused silica capillary column DB-17, 30 m×0.250 mm internal diameter and film thickness of 0.25 μm. The temperatures of the injector and detector were 250°C and 290°C respectively. The oven temperature started at 150°C and increased to 280°C at 6°C per minute. The injection was through a splitless injector, using helium as a carrier gas at a flow rate of 2 mL/min. The run time was 21.67 min. The individual OCPs were identified by comparing the elution time of standard OCPs with those in the samples, whereas each OCP was quantified by comparing the peak areas of the OCPs in the samples with those in standard.

QUALITY ASSURANCE AND QUALITY CONTROL

The blank samples were subjected to the same extraction and clean-up protocols by using the same reagents aside the samples to determine whether any of the studied pesticides was present in the reagents. Analyses of samples were done in triplicates to assure precision of data obtained. In absence of certified pesticide reference materials, recovery experiment was conducted to determine the precision and accuracy of the analytical procedures using standard addition method described by (Sosan et al., 2018). Two portions each of 20 g from each sample was weighed out with one spiked or fortified with 2 μg/kg standard mixture of OCP, whereas the other one was left unspiked. The recovery study results are presented in Table 1 as mean percentage recoveries. The mean percentage recovery values of OCPs ranged from 83.7±1.5 (aldrin) to 97.2±3.9 (lindane) for soil, whereas the values ranged from 75.2±1.6 (chlorothalonil) to 91.8±0.8 (heptachlor epoxide), which were within the range of 70%–120% for acceptable recovery values (European Commission, 2017). The calibration curve of each of each OCP was derived by running up to six serially diluted standard solutions that ranged between 0 and 10 μg/kg. Linearity of calibration curve (R²) was also estimated. The limit of detection and the limit of quantification were estimated, as stated in the following equations:

  

$$\text{Limit of detect}=\frac{3.3s}{b}$$(1),

  

$$\text{Limit of quantification}=\frac{10s}{b}$$(2),

Table 1 Percentage recovery of organochlorine pesticides residues in soil and food crops

Organochlorine Residue	Soil	Food Crop
α-BHC	94.1±3.1	77.9±1.7
β-BHC	88.6±0.9	83.1±3.9
δ-BHC	96.5±1.8	89.5±2.0
Lindane	97.2±3.9	78.4±1.3
Chlorothalonil	90.9±3.3	75.2±1.6
Heptachlor	84.2±4.9	90.7±1.2
Heptachlor Epoxide	89.0±2.6	91.4±0.8
Endosulfan I	92.6±0.7	91.0±4.5
Endosulfan II	87.3±2.9	88.3±2.9
Aldrin	83.7±1.5	79.2±3.1
Endrin	95.5±1.4	86.4±4.6
Dieldrin	83.9±2.1	81.9±0.7
p, p’-DDE	97.0±3.6	76.5±3.8
p, p’-DDT	93.5±1.9	87.8±1.1
Methoxychlor	84.2±0.7	78.3±3.2

where b is the calibration curve slope and s is the residual standard deviation of calibration function (Stock et al., 2016; Adeleye et al., 2019a).

HEALTH RISK ESTIMATION

The health risk assessment of OCP in food crops grown on the floodplains was done by estimating daily intake as well as the hazard indices. The estimated daily intake (EDI) was evaluated using the method of (Oyinloye et al., 2021) stated below:

  

$$EDI=\frac{Cp\times Fc}{Bw}$$(3),

where Cp=pesticide concentration; vegetable consumption rate in Nigeria taken to be 65 g/day (Adedokun et al., 2016); Bw=Average body weight of an adult Nigerian taken to be 60 kg (Oyinloye et al., 2021). The hazard index was evaluated using the method of Adeleye et al. (2019b) stated below:

  

$$\text{HI}=\frac{EDI}{ADI}$$(4),

where EDI is the estimated daily intake and ADI is acceptable daily intake.

RESULTS AND DISCUSSION

The results of pesticides concentrations at the studied sites are presented in Tables 2, 3, 4. Table 2 presents the concentration of organochlorine pesticide residues measured in Irintan floodplain soil. The mean concentration (μg/kg) ranges are as follows: α-BHC (0.23–0.36), β-BHC (BDL-1.85), δ-BHC (0.22–1.85), lindane (0.21–0.33), chlorothalonil (0.97–1.30), heptachlor (0.23–0.58), heptachlor epoxide (0.21–1.78), endosulfan I (0.23–1.88), endosulfan II (BDL-1.32), aldrin (0.22–1.83), endrin (BDL–0.37), dieldrin (BDL-0.54), dichlorodiphenyldichloro ethylene (p,p’-DDE) (BDL-0.45), dichlorodiphenyltrichloroethane (p,p’-DDT) (BDL-1.36) and methoxychlor (0.25–0.84).

Table 2 Concentration of pesticide residues (μg/kg) at Irintan floodplain soil

Parameter	Upper Course			Middle Course			Lower Course
	5 m	25 m	45 m	5 m	25 m	45 m	5 m	25 m	45 m
α-BHC	0.36b±0.02	0.35a±0.06	0.24a±0.03	0.33a±0.00	0.31a±0.02	0.23a±0.05	0.34a±0.01	0.28a±0.03	0.24a±0.03
β-BHC	1.85c±0.31	0.90c±0.00	0.36a±0.09	1.06b±0.20	0.51a±0.00	BDL	0.39a±0.05	0.37b±0.00	0.21b±0.04
δ-BHC	1.85c±0.31	1.09a±0.02	1.57b±0.34	0.44b±0.00	0.22a±0.00	1.05c±0.05	0.67a±0.00	1.04c±0.07	0.93b±0.05
Lindane	0.33c±0.00	0.25b±0.00	0.21a±0.00	0.24a±0.07	0.25a±0.02	0.23a±0.03	0.22a±0.00	0.23a±0.00	0.24a±0.01
Chlorotha	0.97a±0.04	1.09b±0.10	1.30c±0.04	1.18a±0.35	1.15a±0.12	1.05a±0.03	1.08a±0.12	1.10a±0.27	1.02a±0.19
Heptachlor	0.33b±0.07	0.25a±0.00	0.54c±0.02	0.57b±0.19	0.23a±0.00	0.47b±0.06	0.47b±0.03	0.58c±0.00	0.23a±0.02
H/Epoxide	0.30a±0.05	1.60c±0.06	1.08b±0.25	1.78c±0.43	1.47b±0.09	1.30a±0.52	0.21a±0.06	1.43b±0.02	1.34b±0.14
E/sulfan I	0.42c±0.00	0.23a±0.09	0.26b±0.02	0.34b±0.10	0.23a±0.02	1.88b±0.70	0.52c±0.00	0.23a±0.00	0.31b±0.07
E/sulfan II	1.32b±0.11	0.56a±0.02	BDL	BDL	0.29a±0.03	0.03a±0.00	BDL	BDL	0.34a±0.06
Aldrin	0.30a±0.01	1.83c±0.14	0.32b±0.00	0.36a±0.00	1.75b±0.29	0.30a±0.04	0.22a±0.08	0.28a±0.00	1.95b±0.38
Endrin	BDL	0.36a±0.00	0.37a±0.05	0.35a±0.04	0.34a±0.02	BDL	0.35a±0.06	0.34a±0.01	0.32a±0.01
Dieldrin	0.54a±0.03	0.32a±0.00	0.26a±0.00	0.27a±0.03	0.31a±0.01	BDL	0.31a±0.01	0.25a±0.04	0.22a±0.00
p, p’-DDE	0.37b±0.00	0.31a±0.01	BDL	0.35a±0.04	0.34a±0.00	BDL	BDL	BDL	0.45a±0.02
p, p’-DDT	1.36±0.20	0.66±0.12	BDL	BDL	0.59a±0.00	BDL	BDL	0.81a±0.07	0.13b±0.29
Methoxyc	1.33c±0.05	0.78b±0.01	0.59a±0.13	0.34a±0.09	0.53b±0.02	0.84c±0.05	0.49b±0.05	0.49b±0.00	0.25a±0.06

BHC=Benzene hexachloride, Chlotha=Chlorothalonil, H/Epoxide=Heptachlor epoxide, E/sulfan=endosulfan, DDE=Dichlorodiphenyldichloroethene, DDT=Dichlorodiphenyltrichloroethane, Methoxyc=Methoxychlor

Table 3 Concentration of pesticide residues (μg/kg) at Omi-Eye floodplain soil

Parameter	Upper Course			Middle Course			Lower Course
	5 m	25 m	45 m	5 m	25 m	45 m	5 m	25 m	45 m
α-BHC	0.25c±0.01	0.24b±0.00	0.23a±0.00	0.27c±0.00	0.24b±0.03	0.23a±0.01	0.28a±0.07	0.25a±0.00	0.23a±0.02
β-BHC	0.81c±0.00	0.63b±0.01	0.54a±0.15	0.69c±0.07	0.51b±0.18	0.25a±0.00	0.72b±0.00	0.50a±0.09	0.42a±0.01
δ-BHC	1.03b±0.45	0.50a±0.12	0.47a±0.03	1.56b±0.09	1.50b±0.01	1.46c±0.11	0.29b±0.12	0.27b±0.00	0.20a±0.03
Lindane	0.28c±0.06	0.27b±0.03	0.25a±0.00	0.22a±0.00	0.22a±0.00	0.21a±0.05	0.21a±0.00	0.24a±0.00	0.25a±0.07
Chlorotha	150c±0.22	1.38b±0.03	1.17a±0.26	1.58b±0.17	1.36a±0.38	1.34a±0.34	1.27a±0.36	1.22a±0.45	1.18a±0.13
Heptachlor	0.22a±0.22	0.44b±0.06	0.23a±0.04	0.49b±0.03	0.41a±0.09	0.34a±0.00	0.22a±0.07	0.23a±0.03	0.53b±0.00
H/Epoxide	1.51c±0.46	1.34b±0.02	0.26a±0.07	1.66b±0.09	1.86c±0.62	1.23a±0.05	1.75c±0.14	1.30b±0.21	0.33b±0.05
E/sulfan I	0.28a±0.00	1.57c±0.02	1.33b±0.05	1.43b±0.24	1.37b±0.02	0.21a±0.05	1.81c±0.00	1.48b±0.17	0.24a±0.02
E/sulfan II	0.32b±0.00	0.24a±0.03	0.31b±0.07	BDL	0.34a±0.00	BDL	0.33a±0.01	BDL	0.24a±0.00
Aldrin	1.67a±0.26	1.61a±0.21	1.50a±0.02	0.28a±0.01	0.28a±0.05	0.22a±0.01	1.69b±0.47	1.54b±0.03	0.36a±0.02
Endrin	0.40c±0.00	0.36c±0.04	0.33a±0.01	0.35a±0.35	0.38c±0.10	0.37a±0.19	0.56b±0.00	0.40a±0.08	BDL
Dieldrin	0.46c±0.02	0.42b±0.00	0.31a±0.23	0.27a±0.00	0.26a±0.00	0.23a±0.08	0.33a±0.33	BDL	0.22a±0.00
p, p’-DDE	0.33a±0.08	0.25a±0.03	BDL	BDL	0.47a±0.03	BDL	0.98b±0.33	0.38a±0.00	0.45a±0.02
p, p’-DDT	0.87b±0.03	0.81a±0.00	0.79a±0.23	BDL	0.66b±0.02	0.58a±0.12	0.66a±0.12	BDL	0.13b±0.29
Methoxyc	0.60a±0.07	0.74b±0.00	0.76c±0.02	0.75c±0.02	0.66b±0.00	0.47a±0.01	0.39a±0.21	0.73b±0.39	1.17c±0.13

BHC=Benzene hexachloride, Chlotha=Chlorothalonil, H/Epoxide=Heptachlor epoxide, E/sulfan=endosulfan, DDE=Dichlorodiphenyldichloroethene, DDT=Dichlorodiphenyltrichloroethane, Methoxyc=Methoxychlor

Table 4 Concentration of pesticide residues (μg/kg) at Egbigbu floodplain soil

Parameter	Upper Course			Middle Course			Lower Course
	5 m	25 m	45 m	5 m	25 m	45 m	5 m	25 m	45 m
α-BHC	0.24b±0.00	0.25b±0.04	0.31c±0.04	0.24a±0.00	0.23a±0.03	0.22a±0.02	0.27b±0.04	0.26b±0.00	0.22a±0.10
β-BHC	1.35c±0.01	0.50b±0.12	0.41a±0.00	0.46b±0.10	0.40a±0.02	BDL	0.65b±0.14	BDL	0.34a±0.03
δ-BHC	1.92c±0.29	0.64b±0.23	0.41a±0.02	0.81a±0.07	0.97b±0.10	0.95b±0.04	0.44a±0.02	0.45a±0.00	1.40b±0.00
Lindane	0.24b±0.03	0.24b±0.00	0.23a±0.03	0.22a±0.00	0.21a±0.00	BDL	0.26a±0.00	0.25a±0.13	0.23a±0.07
Chlorotha	1.36c±0.60	1.31b±0.14	1.21a±0.44	0.97b±0.23	1.98b±0.12	0.92a±0.04	1.40b±0.66	1.26b±0.20	0.95a±0.39
Heptachlor	0.37b±0.08	0.22a±0.00	0.23a±0.07	0.39c±0.20	0.32b±0.00	0.21a±0.00	0.45b±0.21	0.29a±0.03	0.38b±0.00
H/Epoxide	1.31c±0.04	1.24b±0.32	0.28a±0.00	1.28a±0.01	1.19a±0.83	BDL	0.64b±0.14	0.24a±0.07	1.23c±0.00
E/sulfan I	1.40c±0.07	0.51b±0.13	0.22a±0.05	0.23a±0.00	1.82c±0.25	1.55b±0.34	1.41c±0.30	0.53b±0.04	0.22a±0.00
E/sulfan II	0.39b±0.00	BDL	BDL	0.35a±0.07	BDL	BDL	0.68b±0.09	0.32a±0.00	0.29a±0.00
Aldrin	1.55b±0.14	1.40b±0.09	0.28a±0.00	1.46b±0.57	1.42b±0.22	0.21a±0.00	0.49b±0.00	0.30a±0.00	0.26a±0.03
Endrin	0.37a±0.00	0.36a±0.14	0.39a±0.12	0.21a±0.04	0.33a±0.05	BDL	2.54b±1.20	BDL	0.36a±0.00
Dieldrin	0.27a±0.02	0.28b±0.02	0.35c±0.05	0.28a±0.06	0.25a±0.00	BDL	0.91b±0.27	0.33a±0.01	0.25a±0.05
p, p’-DDE	0.54b±0.00	0.32a±0.00	BDL	0.40a±0.05	0.34a±0.00	BDL	0.99b±0.02	0.43a±0.00	BDL
p, p’-DDT	0.87b±0.06	BDL	BDL	0.70a±0.26	BDL	BDL	0.68b±0.05	0.32a±0.14	0.60b±0.10
Methoxyc	1.73c±0.36	1.43b±0.27	0.69a±0.05	0.59c±0.28	0.46b±0.20	0.30a±0.06	0.88c±0.07	0.23a±0.06	0.48b±0.03

BHC=Benzene hexachloride, Chlotha=Chlorothalonil, H/Epoxide=Heptachlor epoxide, E/sulfan=endosulfan, DDE=Dichlorodiphenyldichloroethene, DDT=Dichlorodiphenyltrichloroethane, Methoxyc=Methoxychlor

Table 3 presents the concentration of organochlorine pesticide residues measured in Omi-Eye floodplain soil. The mean concentration (μg/kg) ranges are as follows: α-BHC, (0.23–0.28), β-BHC (0.25–0.81), δ-BHC (0.20–1.56), lindane (0.21–0.28), chlorothalonil (1.17–1.58), heptachlor (0.22–0.53), heptachlor epoxide (0.26–1.86), endosulfan I (0.21–1.81), endosulfan II (BDL-0.34), aldrin (0.22–1.69), endrin (0.33–0.56), dieldrin (BDL-0.46), p,p’-DDE (BDL-0.98), p,p’-DDT (BDL-0.87) methoxychlor (0.39–1.17).

Table 4 presents the concentration of organochlorine pesticide residues measured in Egbigbu floodplain soil. The mean concentration (μg/kg) ranges are as follows: α-BHC (0.22–0.31), β-BHC (BDL-1.35), δ-BHC (0.41–1.92), lindane (BDL-0.26), chlorothalonil (0.92–1.40), heptachlor (0.21–0.45), heptachlor epoxide (BDL-1.31), endosulfan I (0.23–1.82), endosulfan II (BDL-0.68), aldrin (0.21–1.55), endrin (BDL-2.54), dieldrin (BDL-0.91), p,p’-DDE (BDL-0.99), p,p’-DDT (BDL-0.87) and methoxychlor (0.23–1.73). The range of total OCPs concentration for Irintan soil is 7.50–9.28 μg/kg, Omi-Eye soil is 8.72–9.94 μg/kg and Egbigbu floodplain is 7.33–9.21 μg/kg.

No statistical significant difference exists for most OCP values obtained in soil for upper/middle and lower courses except between middle/lower courses for δ-BHC, upper/middle values for δ-BHC and lindane as well as upper/lower courses for β-BHC at Erio at p<0.05. The t-test shows significant difference exists in the values of aldrin and dieldrin for upper/middle courses at Omi-Eye, whereas no such significance is observed in Irintan and Egbigbu floodplains. Significant difference was noticed in endosulfan II between upper/lower courses and middle/lower courses at Egbigbu. The concentration of heptachlor and heptachlor epoxide (B) detected was the same. The values of chlorothalonil show significance only between upper and middle course at Irintan at p<0.05.

The concentration of parameters such as α-BHC, lindane and dieldrin (upper course) were observed to be decreasing in the order of 5 m>25 m>45 m distances, whereas chlorothalonil (upper course), lindane and aldrin (lower course) decreased in the same order in Irintan river floodplain (Table 2). These phenomena can be attributed to two different sources of contamination. In the first case where the concentration decreases as sampling moves inward into the farm from the river channel/course, the contaminant may have been brought by storm water and got deposited with flood recession, whereas those which concentrations were increasing could be owing to current application of pesticides in the farm. The same trend is observed in Table 3 (Omi-Eye) and Table 4 (Egbigbu). A similar observation was reported by Olawale et al. (2017) in their assessment of level of contaminants in floodplain soils in Ondo State, Nigeria.

The three isomers of benzene hexachloride (BHC) were detected in all samples and floodplains studied. The observed concentration of the three isomers of BHC can be attributed to the use of the γ-isomer (lindane) sold commercially as Gammalin 20, which is the only isomer with insecticidal action. The ratio of β/(α+γ) BHC concentration at each of the three sites (Irintan, Omi-Eye and Egbigbu) was greater than 0.5. This suggests a recent use of the pesticide at the sites (Atuanya and Aborisade, 2017).

Aldrin is easily metabolised to dieldrin. Having been banned from use in Nigeria for close to 2 decades, the OCP ought not to be available in Nigeria market again. However, its detection in this study may suggest its recent use by farmers who may purchase it through marketers who sell pesticides under various trade names or labels or may be added by manufacturers as active ingredients to other pesticides not banned and still in use by Nigerian farmers (Sosan et al., 2020; Oyinloye et al., 2021). The values of endosulfan I at all sites are found to be higher than endosulfan II. This observation is expected because endosulfan II slowly converts to endosulfan I, which is more stable (Sosan et al., 2020). As endosulfan group does not accumulate in the environment like other OCPs, it could therefore be implied that its detection on the floodplains indicates its recent use. The level of the epoxide may be directly related to the application of heptachlor on the farm because heptachlor is only converted to heptachlor epoxide in plant and insect tissue with the heptachlor epoxide being more chemically potent than the heptachlor itself. Of all OCP residues detected, chlorothalonil has the highest concentration at Omi-Eye and Egbigbu floodplains while its value is the second highest at Irintan. This may suggest chlorothalonil as the most popular among the OCPs in the study area. The result of this study reveals no particular trend in the values of DDT over those of DDE and methoxychlor in all the sites. The total OCP is in the following order: Omi-Eye>Egbigbu>Irintan.

The fact that all OCP parameters tested detected show that the pesticide is commonly used by farmers on the floodplains. This is against the ban placed on the use of OCPs in Nigeria. The reasons for their continued use in most developing countries including Nigeria are high efficacy/potency, lower cost when compared with alternative pesticides and weak/non-enforcement of ban by regulatory authorities. Exposure to organochlorine pesticides over a short period may produce convulsions, headache, dizziness, nausea, vomiting, tremors, confusion, muscle weakness, slurred speech, salivation and sweating. Long-term exposure to organochlorine pesticides may damage the liver, kidney, central nervous system, thyroid and bladder (ASTDR, 2024; CDC, 2024; EPA, 2024). Many of these pesticides have been linked to elevated rates of liver or kidney cancer in animals and humans (Manfo-Tsagué et al., 2020). There is some evidence indicating that organochlorine pesticides may also cause cancer in humans. The continued use of OCPs has remained a matter of international concern because of their persistence and long-distance carriage through oceanic currents and atmospheric transports (Zheng et al., 2020).

The results show that the residues levels are obviously lower when compared with other agricultural soil (Atuanya and Aborisade, 2017; Gakuba et al., 2019; Oyinloye et al., 2021). The mean OCP concentrations in this study are however higher than those reported by Olayinka et al., 2013.

The low pesticide residues concentration in all study sites may be owing to the fact that the lands are not cultivated continuously. Like traditional African farming system, the land is allowed to fallow for some years after which they are used again.

Table 5 presents the organochlorine pesticide residues levels at the studied farms in comparison with other farms in Nigeria. The values obtained in this study are far lower than the values obtained at Minna and Abuja farms in Northern Nigeria. However, the values obtained at Ile-Oluji farm in Southern Nigeria is comparable with those obtained at the studied farms. The large values at Minna and Abuja farms may imply recent and large usage of organochlorine pesticides by the farmers against the ban placed on it by the United Nations.

Table 5 Mean concentration of organochlorine pesticide residues at the studied farms in comparison with other farms in Nigeria (μg/kg)

Parameters	Irintan	Omi-Eye	Egbigbu	Ile-Olujia	Minnab	Abujac
α-BHC	0.30±0.05	0.25±0.01	0.25±0.03	0.13±0.03	BDL	1,690±340
β-BHC	0.63±0.56	0.56±0.17	0.45±0.39	0.20±0.11	NT	2,420±670
δ-BHC	0.98±0.51	0.81±0.57	0.89±0.50	0.09±0.03	NT	NT
Lindane	0.24±0.03	0.24±0.02	0.21±0.07	NT	BDL	NT
Chlorothalonil	1.10±0.09	1.33±0.14	1.15±0.32	NT	NT	NT
Heptachlor	0.41±0.14	0.35±0.12	0.31±0.08	BDL	BDL	2,370±170
Heptachlor Epoxide	1.17±0.55	1.25±0.58	0.82±0.53	NT	NT	NT
Endosulfan I	0.49±0.53	1.08±0.64	0.87±0.65	BDL	NT	NT
Endosulfan II	0.28±0.43	0.19±0.15	0.22±0.24	0.02±0.01	50.0±30	NT
Aldrin	0.81±0.77	1.02±0.69	0.78±0.61	0.01±0.01	NT	2,210±235
Endrin	0.27±0.15	0.35±0.14	0.51±0.76	0.05±0.02	NT	4,458±572
Dieldrin	0.28±0.13	0.27±0.13	0.32±0.24	0.37±0.28	BDL	NT
p,p-DDE	0.20±0.19	0.32±0.31	0.33±0.32	0.94±0.01	NT	NT
p,p-DDT	0.39±0.48	0.50±0.35	0.35±0.36	0.27±0.02	290.0±40	2,750±560
Methoxychlor	0.63±0.32	0.70±0.22	0.75±0.51	NT	NT	NT

NT=Not Tested, BDL=Below Detection Limit

a=Okoya et al., 2013; b=Ogbonaya et al., 2017; c=Dan-Kishiya et al., 2023

Table 6 presents mean pesticide concentration at Irintan, Omi-Eye and Egbigbu farms in comparison with their controls. As can be observed at Irintan floodplain, most of the OCP parameters tested for were not detected in the control samples unlike farm site soils. The trend is the same at Omi-Eye and Egbigbu. This suggests that the farm sites were more polluted than their controls. This observation can be attributed to flooding of the farm sites, which may probably deposit pollutants, including pesticides bought down as a result of runoff from nearby farms after the recession of the flood plus the anthropogenic activities on the farm itself.

Table 6 Mean pesticide concentration at Irintan, Omi-Eye and Egbigbu farms in comparison with their controls

	Irintan		Omi-Eye		Egbigbu
	Farm	Control	Farm	Control	Farm	Control
α-BHC	0.30±0.09	BDL	0.25±0.15	BDL	0.25±0.11	BDL
β-BHC	0.57±0.01	0.21±0.11	0.56±0.29	BDL	0.46±0.03	0.20±0.03
δ-BHC	0.24±0.03	BDL	0.24±0.05	BDL	0.21±0.13	0.18±0.15
Chlorothalonil	0.86±0.10	BDL	1.33±0.59	0.25±0.07	1.15±0.52	BDL
Lindane	0.98±0.25	BDL	0.81±0.32	0.33±0.20	0.88±0.06	0.72±0.05
Heptachlor	0.41±0.02	BDL	0.35±0.08	BDL	0.32±0.01	BDL
Aldrin	0.81±0.14	BDL	1.00±0.21	0.53±0.09	0.82±0.23	BDL
Heptachlor Epoxide (B)	1.20±0.55	0.15±0.03	1.25±0.72	BDL	0.82±0.09	0.28±0.11
Endosulfan I	0.49±0.07	0.17±0.12	1.08±0.15	BDL	0.88±0.27	BDL
p, p’-DDE	0.20±0.12	BDL	0.30±0.22	BDL	0.34±0.20	0.22±0.01
Dieldrin	0.27±0.02	BDL	0.33±0.04	BDL	0.33±0.08	BDL
Endrin	0.27±0.20	BDL	0.39±0.10	BDL	0.52±0.37	BDL
Endosulfan II	0.31±0.09	BDL	0.17±0.12	BDL	0.23±0.10	BDL
p, p’-DDT	0.51±0.33	0.34±0.25	0.48±0.06	BDL	0.35±0.19	BDL
Methoxychlor	0.63±0.16	0.19±0.01	0.70±0.19	BDL	0.75±0.43	0.25±0.19

Table 7 presents the result of pesticide residues concentration in food crops at the three sites. The mean ranges at Irintan, Omi-Eye and Egbigbu floodplain respectively are: α-BHC (0.62–2.50), (0.50–2.80), (0.66–4.76); β-BHC (1.01–3.93), (1.11–4.40), (3.39–7.16); δ-BHC (1.70–4.11), (0.75–388), (1.57–11.52); lindane (0.82–1.64), (0.62–2.45), (0.78–5.68); chlorothalonil (1.02–1.09), (1.13–8.24), (0.43–16.20); heptachlor (0.82–2.50), (0.59–2.92), (0.72–4.16), heptachlor epoxide (1.04–3.56), (0.59–1.98), (BDL–1.66) endosulfan I (BDL-1.64), (0.49–2.85), (1.07–6.58); endosulfan II (1.07–3.12), (0.40–4.25), (0.45–2.02); aldrin (0.46–5.56), (1.56–3.33), (2.43–32.12); endrin (1.00–3.33), (0.64–5.73), (BDL-4.02); dieldrin (1.61–1.98), (1.45–2.96), (BDL-6.59); p, p’-DDE (0.64–1.97), (0.36–4.30), (BDL-1.66); p,p’-DDT (3.07–4.74), (0.85–5.02), (0.72–13.72); and methoxychlor (1.83–7.78), (0.68–7.65), (0.60–5.96); TOCP (21.35–34.18), (12.05–51.89), (19.42–107.48). The result reveals no particular trend in the values. However, a look reveals that the highest OCP concentration in Irintan is p, p’-DDT in Talinum triangulare and Zea mays, whereas methoxychlor is the highest in Caspicum annum.

Table 7 Concentration of pesticide residues (μg/kg) in food crops cultivated on Irintan, Omi-Eye and Egbigbu floodplains

Locations	Irintan			Omi-Eye			Egbigbu
Food Crops	Veg.	Pepper	Maize	Veg.	Pepper	Maize	Veg.	Pepper	Maize
α-BHC	2.50c±0.49	1.91b±0.05	0.62a±0.00	1.64b±0.24	2.80c±0.16	0.50a±0.06	4.76a±2.33	1.67b±0.63	0.66a±0.10
β-BHC	3.93c±0.08	1.01a±0.25	2.25b±0.06	4.40b±0.65	1.22a±0.47	1.11a±0.03	7.16c±0.28	5.08b±0.05	3.39a±0.17
δ-BHC	4.11b±0.05	4.62b±0.10	1.70a±0.03	3.83c±0.53	3.88c±0.07	0.75a±0.00	11.52c±5.79	3.84b±0.55	1.57a±0.04
Lindane	1.64b±0.00	1.54b±0.07	0.82a±0.14	2.45c±0.07	1.88b±0.39	0.62a±0.17	5.68c±0.12	2.19b±0.05	0.78a±0.00
Chlorotha	1.02b±0.24	1.09b±0.19	1.06b±0.00	8.24c±1.29	2.48b±0.93	1.13a±0.06	16.20b±3.39	0.74a±0.11	0.43a±0.20
Heptachlor	2.50c±0.64	1.68b±0.21	0.82b±0.02	2.92c±1.03	1.82b±0.79	0.59a±0.02	4.16c±1.62	1.18b±0.97	0.72a±0.03
H/Epoxide	1.51b±0.02	3.56c±0.77	1.04a±0.00	0.59a±0.20	1.98b±0.75	0.81a±0.03	BDL	1.66a±0.00	1.58a±0.03
E/sulfan I	1.64a±0.30	BDL	1.55a±0.00	2.81b±0.00	2.85b±0.73	0.49a±0.03	6.20b±4.79	6.58b±0.79	1.07a±0.31
E/sulfan II	1.07a±0.02	3.12b±0.11	1.09a±0.54	3.15b±1.13	4.25c±2.09	0.40a±0.00	1.07a±0.05	2.02b±0.67	0.45a±0.20
Aldrin	2.38b±1.50	5.56b±1.74	0.46a±0.10	1.56a±0.47	3.33b±0.95	1.63a±0.29	32.12c±7.09	4.76b±1.99	2.43a±0.69
Endrin	1.73b±0.09	3.32c±0.56	1.00a±0.04	5.73c±1.76	3.82b±0.35	0.64a±0.19	BDL	4.02b±0.25	1.28a±0.83
Dieldrin	1.61a±0.08	1.84a.b±0.37	1.98c±0.23	2.96b±0.59	2.42b±0.00	1.45a±0.06	BDL	6.59b±0.93	1.26a±0.77
p, p’-DDE	1.97b±0.63	1.68b±0.00	0.64a±0.04	1.60b±0.00	4.30c±2.13	0.36a±0.07	BDL	1.22a±0.00	1.66a±0.09
p, p’-DDT	4.74b±0.05	3.07a±0.02	3.42a±0.00	1.51c±0.00	5.02c±1.65	0.85a±0.30	13.72c±0.39	0.72a±0.00	1.54a±0.21
Methoxyc	1.83a±0.39	7.78c±0.03	3.19a±0.01	7.65b±2.58	0.84a±0.15	0.68a±0.09	5.96b±3.07	0.83a±0.62	0.60a±0.02
TOCP	34.18b±1.09	41.75b±1.94	21.35a±0.89	51.89b±2.11	42.06b±1.15	12.05a±0.36	107.48b±8.33	43.10a±2.02	19.42a±0.77

BHC=Benzene hexachloride, Chlotha=Chlorothalonil, H/Epoxide=Heptachlor epoxide, E/sulfan=endosulfan, DDE=Dichlorodiphenyldichloroethene, DDT=Dichlorodiphenyltrichloroethane, Methoxyc=Methoxychlor, Veg.=Vegetable (Talinum triangulare), Pepper=Caspicum annum, Maize=Zea mays

At Omi-Eye, it is chlorothalonil in Talinum triangulare and Zea mays, whereas it is p,p-DDT in Caspicum annum. At Egbigbu, it is chlorothalonil in Talinum triangulare and β-BHC in Caspicum annum and Zea mays. However, the values obtained in this study are generally lower than the maximum residue limits (FAO/WHO, 2020). The total OCP is in the following order: Caspicum annum>Talinum triangulare>Zea mays at Irintan, Talinum triangulare>Caspicum annum>Zea mays at Omi-Eye, whereas it is Talinum triangulare>Caspicum annum>Zea mays at Egbigbu. The detection of the residues in the food crops may be because of the recent use of the organochlorine pesticides by the farmers. Government may therefore need to educate farmers and the general public on the need to stop the use of the banned pesticides.

Table 8 presents the result of EDI (μg/kg/day) in food crops obtained at the three sites. As revealed by the Table, all estimated values are lower than the WHO/FAO recommended average daily intake. This is a welcome development as consumers may not be at risk in consuming the food crops over a life time.

Table 8 Estimated daily intake for food crops cultivated on Irintan, Omi-Eye and Egbigbu floodplains

Locations	Irintan			Omi-Eye			Egbigbu			WHO/FAO/ADI (μg/kg/day)
Food Crops	Veg.	Pepper	Maize	Veg.	Pepper	Maize	Veg.	Pepper	Maize
α-BHC	2.70E-3	2.06E-3	6.70E-4	1.77E-3	3.03E-3	5.40E-3	5.16E-3	1.80E-3	7.13E-4	0.50
β-BHC	4.24E-3	1.09E-3	2.43E-3	4.75E-3	1.32E-3	1.20E-3	7.73E-3	5.49E-3	3.66E-3	0.50
δ-BHC	4.44E-3	4.11E-3	1.84E-3	4.19E-3	2.83E-3	8.53E-4	1.24E-2	4.15E-3	1.70E-3	0.50
Lindane	1.77E-3	1.66E-3	8.86E-4	2.65EE-3	2.03E-3	6.70E-4	6.13E-3	2.37E-3	8.42E-4	0.30
Chlorotha	1.10E-3	1.15E-3	8.32E-3	8.90E-3	2.68E-3	1.22E-3	1.75E-2	7.99E-4	4.64E-4	NA
Heptachlor	2.70E-3	1.81E-3	8.86E-4	3.15E-3	1.97E-3	6.37E-3	4.49E-3	1.22E-3	7.78E-4	0.10
H/Epoxide	1.63E-3	3.84E-3	1.12E-3	1.46E-3	2.14E-3	8.75E-4	—	1.79E-3	1.71E-2	0.10
E/sulfan I	1.77E-3	—	1.67E-3	3.08E-3	3.54E-3	5.29E-4	6.70E-3	7.11E-3	1.16E-3	0.05
E/sulfan II	1.56E-3	3.37E-3	1.18E-3	3.40E-3	4.59E-3	4.32E-4	—	2.18E-3	4.86E-4	0.05
Aldrin	2.57E-3	6.00E-3	4.97E-4	1.68E-3	3.60E-3	1.76E-3	3.47E-2	5.14E-3	2.62E-3	0.10
Endrin	1.87E-3	3.59E-3	1.08E-3	6.19E-3	4.13E-3	6.91E-4	—	4.34E-3	1.38E-3	0.10
Dieldrin	1.74E-3	1.99E-3	2.14E-3	3.20E-3	2.61E-3	1.57E-4	—	7.12E-3	1.36E-3	0.10
p, p’-DDE	2.13E-3	1.81E-3	6.91E-4	1.73E-3	4.64E-3	3.89E-4	—	1.32E-3	1.79E-3	0.05
p, p’-DDT	5.12E-3	3.32E-3	3.69E-3	1.63E-3	5.42E-3	9.18E-4	1.48E-2	7.79E-4	1.66E-4	0.05
Methoxyc	1.98E-3	8.40E-3	3.45E-3	8.26E-3	9.07E-4	7.34E-4	6.44E-3	8.96E-4	6.48E-4	NA

BHC=Benzene hexachloride, Chlotha=Chlorothalonil, H/Epoxide=Heptachlor epoxide, E/sulfan=endosulfan, DDE=Dichlorodiphenyldichloroethene, DDT=Dichlorodiphenyltrichloroethane, Methoxyc=Methoxychlor, Veg.=Vegetable (Talinum triangulare), Pepper=Caspicum annum, Maize=Zea mays, NA=Not available

Table 9 presents the result of estimated hazard indices for the food crops obtained at the three sites. It could be observed from the Table that all values are less than 1. This implies the food crops may pose no hazard to the consumers of the food crops (Adedokun et al., 2016), which is equally welcome.

Table 9 Estimated hazard indices for food crops cultivated on Irintan, Omi-Eye and Egbigbu floodplains

Locations	Irintan			Omi-Eye			Egbigbu
Food Crops	Veg.	Pepper	Maize	Veg.	Pepper	Maize	Veg.	Pepper	Maize
α-BHC	5.40E-3	4.12E-2	1.34E-2	3.54E-3	6.04E-3	1.08E-2	1.03E-2	3.60E-3	1.43E-3
β-BHC	8.48E-3	2.18E-3	4.86E-3	9.50E-3	2.64E-3	3.60E-3	1.55E-2	1.10E-2	7.32E-3
δ-BHC	8.88E-3	9.98E-3	3.68E-3	8.38E-3	5.66E-3	1.71E-3	2.48E-2	8.30E-3	3.40E-3
Lindane	5.90E-3	5.53E-3	2.95E-3	8.83E-3	6.77E-3	2.23E-3	2.04E-2	7.90E-3	2.81E-3
Chlorotha	—	—	—	—	—	—	—	—	—
Heptachlor	2.70E-2	1.81E-3	8.86E-3	3.15E-2	1.97E-2	6.37E-2	4.49E-2	1.22E-2	7.78E-3
H/Epoxide	1.63E-2	3.84E-2	1.12E-2	1.46E-2	2.14E-2	8.75E-3	—	1.79E-2	1.71E-2
E/sulfan I	3.54E-3	—	3.34E-2	6.16E-3	7.08E-3	1.06E-2	1.34E-2	1.42E-2	2.32E-3
E/sulfan II	3.12E-3	6.74E-3	2.36E-3	6.80E-3	9.18E-3	8.64E-3	—	4.36E-3	9.72E-4
Aldrin	2.57E-2	6.00E-3	4.97E-3	1.68E-2	3.60E-2	1.76E-2	3.47E-1	5.14E-2	2.62E-2
Endrin	1.87E-2	3.59E-2	1.08E-2	6.19E-2	4.13E-2	6.91E-3	—	4.34E-2	1.38E-3
Dieldrin	1.74E-2	1.99E-2	2.14E-2	3.20E-2	2.61E-2	1.57E-3	—	7.12E-2	1.36E-2
p, p’-DDE	4.26E-3	3.62E-3	1.38E-2	3.46E-3	9.28E-3	7.78E-4	—	2.64E-3	3.58E-3
p, p’-DDT	1.02E-2	6.64E-3	7.38E-3	3.26E-3	108E-2	1.84E-2	2.96E-2	1.56E-3	3.32E-03
Methoxyc	—	—	—	—	—	—	—	—	—

BHC=Benzene hexachloride, Chlotha=Chlorothalonil, H/Epoxide=Heptachlor epoxide, E/sulfan=endosulfan, DDE=Dichlorodiphenyldichloroethene, DDT=Dichlorodiphenyltrichloroethane, Methoxyc=Methoxychlor, Veg.=Vegetable (Talinum triangulare), Pepper=Caspicum annum, Maize=Zea mays

CONCLUSION

This study showed that some banned pesticides especially the benzene hexachloride and endosulfan isomers were still being used by the farmers at the study sites, which is against the prevailing government regulation. This study equally revealed that pesticide residue concentrations were lower than the maximum residue levels. Therefore, regulatory authorities at federal and state government levels in Nigeria especially the National Environmental Standards and Regulations Enforcement Agency and Ekiti State Environmental Protection Agency should conduct regular checks on the environment in order to enforce the ban of OCPs so as to have a sustainable environment. Agricultural Extension Officers should equally be directed by government to assist in educating farmers on the need to stop the use of the banned pesticides.

ACKNOWLEDGEMENTS

The authors would like to thank the staff of the Department of Chemistry, Federal University of Technology, Akure, Nigeria, for their useful pieces of advice and technical assistance during the laboratory work. We are equally indebted to the anonymous reviewers for their constructive comments that have improved the manuscript greatly.

CONFLICTS OF INTERESTS

The authors declare that they have no known competing commercial/financial interest or personal relationships that could have appeared to influence the work reported in this paper.

AVAILABILITY OF DATA AND MATERIALS

This is not applicable to this work as all the data reported in the paper were generated from the study and other data not generated directly were duly referenced.

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