Ecological and Human Health Risk Assessment of Pesticide Residues in Fish and Sediments from Vea Irrigation Reservoir

The low yield of food production ascribed to harm caused by pests has led to the application of pesticides to food crops. Pesticide residues from the application on crops are mostly found in foods that can cause diseases for consumers of such products. A total of 37 pesticide residues consisting of 15 organochlorines (OC), 13 organophosphorus (OP) and 9 synthetic pyrethroids (SP) were determined. The QuEChERS method was exploited for extraction and clean-up. Gas Chromatograph was used for detection and quantifica-tion which was equipped with an electron capture detector and pulse flame photometric detector. The results showed that the mean concentrations of pesticides in fish ranged from 0.007 mg·kg −1 to 1.026 mg·kg −1 for OCs, 0.002 mg·kg −1 to 0.190 mg·kg −1 for OPs and 0.004 mg·kg −1 to 0.032 mg·kg −1 for SP. Sediments have mean concentrations ranged from 0.005 mg·kg −1 to 1.207 mg·kg −1 for OCs. OP ranges from 0.002 mg·kg −1 to 0.399 mg·kg −1 and 0.003 mg·kg −1 to 0.202 mg·kg −1 for synthetic pyrethroids. Maximum Residue Limits were exceeded in both fish and sediment samples except for malathion, fenitrothion, profenofos, gamma-chlordane, and deltamethrin. Exposure in children ranged from 4.60 × 10 −6 mg·kg −1 ·d −1 to 2.36 × 10 −3 mg·kg −1 ·d −1 and in adults it is from 1.97 × 10 −6 mg·kg −1 ·d −1 to 1.01 × 10 −3 mg·kg −1 ·d −1 . Health risk estimation revealed a non-cancer risk potential of β-HCH in sediment and aldrin and p,p'-DDE in fish. Carcinogenic risk assessed for organochlorine pesticide residues indicates cancer benchmark concentrations greater than 10 −4 to 10 −6 threshold for acceptance.


Introduction
Pesticides are widely used in agricultural and sanitation sectors for combating pests in Ghana [1]. The use of pesticides in agricultural lands to control pests brings about bumper harvest to farmers whiles producing toxics to non-target organisms [2] such as fish [3]. Pesticide usage in Ghana continues to increase as agricultural production escalates. This increase in pesticide usage brings with it environmental and health ills arising from indiscriminate use and inappropriate handling of the chemicals. Workers exposed to pesticide are often illiterate and lack training, no right equipment and adequate safety information. Lack of legislative controls, susceptible population and the availability of highly toxic pesticides which often are poorly labelled and badly package and irresponsibly promoted are serious factors accounting for the hazards of pesticide use in Ghana [4]. The toxic, persistent pesticides may spread within the reservoir deteriorating the quality of the water gradually jeopardizing its use for drinking by humans and livestock. Non-target flora and fauna concentrate these chemicals in their tissues and pass them on along the food chain. The accumulation of such pollutants in food chain may restrict the consumption of valuable food resource like fish [5].
Modern agriculture relies to a great extent on pesticides application to feed the ever growing large populations around the world [6]. Humans and the environment are exposed to several dangers from long and increased use of pesticides [7]. A well planned and enacted legislation and massive pressure from environmentalists is essential for the enforcement and supervision of pesticides use [8]. This will help obtain high benefits with very low risk to humans and the environment [9]. Approximately 87% of Ghanaian farmers use chemical pesticides to control pests and diseases on vegetables and fruits [10]. The risk posed by pesticide residues to humans and the environment varies with the toxicological, physical and ecological properties of the pesticide. In Ghana, fresh or processed fish is a major source of protein for both humans and animals [1]. The USA uses about 5 million kg of pesticides each year with agriculture accounting for 70% -80% of the total pesticide use [11].
The risk posed by pesticides to aquatic life is relative and depends on several factors including landscape, application method, application rate, erosion, irrigation, topography, soil type and land management practices [12]. Sea foods such as fish, lobsters, prawns, mussels and oysters are generally classified as a rich source of protein and other nutrients [13]. Invariably, an increase in concentrations of pesticide residues in fish and sediments, is an indication of the high level of pollution of the water throughout its food web [14].
The use OCs and many different kinds of OPs have been banned in Ghana, yet they are still in use by many farmers across the country. This is because they are still effective in the control of pests and relatively inexpensive compared to the legally allowed once [4].
The increase presence of pesticide residuals around the catchment area of the

Description of Study Area
Vea is a community under the Bongo District of the Upper East Region of Ghana. The Vea reservoir is located between latitude 10˚45'N and longitude 1˚W.
The vegetation in the study area is dry guinea savannah, distinguished by short grasses and short trees. The climate has a mean minimum and maximum temperature of 14˚C and 40˚C, respectively. The mean annual rainfall ranges from 850 to 1000 mm which occurs in the months from May to October, followed by a prolonged dry season [15]. The first part of the dry season from November to mid-February is characteristically cold and dry with dusty Harmattan winds. The rest of the dry season is usually characterized by a wide temperature range from 14˚C at night and to over 35˚C during the day. Humidity is also very low, making the daytime temperature high and less comfortable. The Vea irrigation project is constructed on the tributary of the White Volta River from Burkina Faso and serves eight communities with a total farmer population of 6000 as shown in

Sampling
Three different fish species; tilapia (Oreochromis niloticus), sardi (Alestes baremose) and African catfish (Clarias gariepinus) were considered for this work, because they are the most frequently eaten in the study area. A total of seventy-five (75) fish samples, twenty-five (25) each were purchased from fishermen at the landing site of the reservoir with another twenty-five (25) sediment samples which were evenly taken from different parts of the reservoir.
The fish samples were first wrapped in aluminum foil and packed in labelled clean polyethylene bags as with the sediment samples and transported in thermos-insulated containers with ice packs to the laboratories of KNUST where they were stored at temperature below −10˚C until processed.

Sample Preparation and Extraction
The sediment samples were air dried for one week. Stalks, stones and other debris were removed and each sample homogenized to maintain homogeneity.
These samples were then ground and passed through a 2 mm sieve to remove the coarse sediment fraction and kept in plastic bags. Ten (10.0) g of homogenous fish sample was weighed into a 250 mL nalgene jar and 50 mL acetonitrile was added and macerate for 2 min. Centrifugation was done for 3 min at 3000 turns/min. The extract was then filtered through a filter paper into a 100 mL volumetric flask. Another (20 mL) acetonitrile was added to the residue, macerated for 1min and the dispersing element rinsed with acetonitrile into the jar and centrifuged for 3 min. at 3000 turns/min. The residue was filtered again into the 100 mL volumetric flask, and the jar rinsed for residue with acetonitrile and adjusted the filtrate to the 100 mL mark. Fifty (50) mL residue was transferred into a round bottom flask, and concentrated on the rotary evaporator to 2 mL for adsorption chromatography.

Sample Clean-Up in Fish Extract
A Bond Elute C-18 was conditioned with a 1000 mg/6mL cartridge with (6 mL) acetonitrile and the sample extract were poured into the column and the column eluted with 10 mL acetonitrile. A Silica SPE cartridge was conditioned with 1000 mg/6mL which has 2 g of MgSO 4 on top with (6 mL) acetonitrile. The extract

Extraction of Pesticide Residues in Sediment
Ten (10.0) g of homogenous sediment sample was put in a 100 mL separating flask and 10 mL acetonitrile added, corked and sonicated for 5 min. After that, a further 10 mL acetonitrile was added, corked and the flask place on the horizontal mechanical shaker and set to shake continuously for 30 min. The mixture was allowed to stand for 10 minutes to separate into layers. Ten (10) mL of the organic phase was pipetted into a round-bottomed flask and evaporated to 2 mL for extract clean-up.

Sample Clean-Up in Sediment
A cartridge was conditioned with silica and acetonitrile (1000 mg/6mL) to have a 1 cm thickness layer of anhydrous magnesium sulphate on top with (10 mL) of acetonitrile. Two (2) mL of the extract was purified by loading onto the cartridge and the eluate collected into a flask. The cartridge was further eluted with 10 mL of acetonitrile and the filtrate concentrated below 40˚C on the rotary evaporator.
The filtrate was re-dissolved in 1 mL ethyl acetate and the extract transferred into a 2 mL, standard vial prior to quantitation by GC-ECD.

Quality Control Analysis
The quality of analysis of pesticide residues was enhanced through solvent blanks and spikes. The solvent blanks were used to check for interferences from reagents, whilst the spike samples were used to determine recovery which is an indicator of method performance and accuracy. The triplicate and duplicate measurements of samples were used to confirm method precision. The recoveries ranged between 74% -120% for organochlorine pesticide residues, 70% -94% for organophosphorus pesticide residues and 73% -100% for synthetic pyrethroid pesticide residues. Fortification level of 0.05 mg/kg was chosen for OCs in sediment samples and 0.01 mg/kg for fish samples based on the limit of determination of the pesticides being analysed. A gas chromatogram, Varian CP-3800 equipped with 63Ni electron capture detector, CTC Analytic Combi PAL autosampler, split-splitless injector, programme pneumatic control and a computer star workstation data processor were used for all classes of pesticides.

Estimation of Exposure to Humans and Risk
The estimated daily exposure (Ems) of individuals to pesticide residues from each fish species was determined using Equation (1); where Cm, CR˚ and BW represent concentration of chemical contaminant in the muscle portion of fish (mg/kg), mean daily consumption rate of fish (kg/d) [17] and body weight of an individual consumer (kg) [18]. The estimated daily exposures are calculated for children and adults eating contaminated fish species of tilapia, catfish and sardi as shown in Table 1 for OPs, Table 2 for OCs and Table 3 for SPs.
When HI is less than 1.0 it can be concluded with great certainty that there is essentially no probability of population or community level effect. However, if the ratio exceeds 1.0 then there is a potential for adverse effect of either carcinogenic or non-carcinogenic risk. Carcinogenic risk ( CR ) were estimated using the Equation (3); where Em and SF represents the estimated exposure and slope factor.  Table   4 to estimate risk sediments pose to fish species.
The human health risk assessment of consumers of contaminated fish by pesticides is calculated for children and adults using the Hazard Indices. Table 5 and Table 6 show Hazard Indices of OPs and SPs respectively. There is no certainty of potential adverse effect of cancer or non-cancer effects.       Residues of fourteen (14)

Ecological Risk Assessment of Fish and Sediment Samples
The benchmark concentration for carcinogenic effect was derived using USEPA cancer slope factor and the exposure concentration and also for non-carcinogenic effect. Risk assessments were conducted based on the concentrations of OC, OPs and SPs pesticides residues in fish tissues and in sediment. Hazard Indices (HIs) were calculated by dividing the average daily exposure by the reference dose concentrations for fish samples and Risk Quotients were by dividing measured environmental concentrations by predicted no effect concentrations [19]. A hazard ratio which is greater than unity indicates that the average exposure level From [20], Risk quotient method (RQ) was used to determine the risk sediments pose to aquatic organisms e.g. fish species. RQ is the ratio of the Predicted

Environmental Concentration (PEC) to the Predicted No Effect Concentration
(PNEC) [21]. The PNEC was estimated by dividing the LC 50 with an assessment factor (AF) of 100 [22]. AF is the total uncertainty factor which is from the product of the assumption that the least sensitive humans are 10 times more sensitive than the most sensitive animal species and the additional uncertainty factor of 10 is used to address differences in sensitivity among humans (this is from the assumption that the most sensitive human is 10 times more sensitive than the least sensitive human). This results in a total uncertainty factor of 100 as AF [23]. The results of RQ estimations from PEC (MEC) and (PNEC) [24] the various pesticides residues are calculated.

Carcinogenic Human Risk
The [27] has defined acceptable risks for carcinogens as within the range 10 −4 to 10 -6 excess lifetime cancer risk. Carcinogenic health risk was calculated for OCs pesticide residues because of their possible cause of cancer to humans. The cancer benchmark concentrations were derived using the oral slope factors (OSFs) of OCs pesticide residues [28]. From [29], individuals have up to a one in between 10,000 to 1,000,000 chance of not developing cancer in their lifetimes; anything short predisposes humans to cancer risk effects.

Potential Health Risk Associated with the Consumption of Fish Contaminated with OC, OP and SP Residues from Vea Reservoir
The Risk Quotient (RQ) values presented in Table 4  The Hazard Indices in Tables 5-7 showed that aldrin and p,p'-DDE recorded HI > 1. This establishes that there is health risk associated with lifetime consumption of catfish, tilapia and sardi from Vea reservoir. All other pesticides in catfish, tilapia and sardi showed no health hazard associated with their consumption as their Hazard Indices for all the detected residues were < 1 in spite of their presence in fish. The Oral Slope Factor (OSF) determines the chance of or not developing cancer in the lifetime of a person exposed to contaminated fish.

Conclusions and Recommendation
This research has identified the presence of persistent, bio-accumulative and toxic pesticide residues in fish and sediment at levels that raise public health concerns.
This study has also revealed the presence of β-HCH, aldrin and p,p'-DDE in fish and sediment in concentrations above acceptable detectable levels by WHO/ FAO with corresponding non-cancer and cancer risk values. Analysis of health risk assessment exposed systematic toxicity to the ecology and consumers of fish from the Vea reservoir in their lifetime.
Health risk assessment conducted for detected OPs and SPs indicated that these pesticide residues did not pose a non-cancer health threat to children and adults. Cumulative risk assessment of OPs and SPs pesticide mixtures in sampled fish did not also present any health threat.
Non-cancer health risk assessment for OCs pesticides indicated that the estimated Hazard Indices for aldrin and p,p'-DDE were greater than 1 in both children and adults from samples of catfish, tilapia and sardi fish indicating potential adverse human health effects. Carcinogenic risk assessed for OCs pesticide residues indicated that aldrin and p,p'-DDE have cancer benchmark concentrations greater than 10 −4 to 10 −6 threshold for acceptance. Hence there is the possible carcinogenicity in lifetime of consumers of contaminated fish from the Vea re- servoir.
An immediate reinforcement of the ban on the use of OCs for irrigation and fishing at the reservoir while pragmatic measures are engaged to stop the consumption of fish from the reservoir is needed by government.