Pesticide and Nutrient Loads of Lake Bosomtwe in the Ashanti Region of Ghana

Pollution of Lake Bosomtwe is a major concern in Ghana due to its derived so-cio-economic benefits such as employment, ecotourism and major protein source to the people in the basin. Besides these benefits, the lake water is used for domestic purposes and has since served as the drinking water source to the people. However, the use of agrochemicals within the basin has intensified within the last decade. The problems associated with fertilizer and pesticide use in the Bosomtwe basin seem to carry with it a higher price, which, if not identified and checked, will overshadow the desired benefits of the lake. This study assesses pesticide and nutrient loads of Lake Bosomtwe in the Ashanti Region of Ghana. Fifty-four (54) lake water samples were collected from September 2016 to February 2017. Pesticide samples were extracted using the solid phase extraction method and GCMS to identify the pesticides present in the water samples and determine their loads. The data obtained were analyzed using Statistical Product Service Solutions (SPSS version 20) for descriptive statistics. The concentration of dichlorvos was


Introduction
Lakes are vulnerable, and their overall condition is deteriorating globally [1]. Pollution of Lake Bosomtwe is a major concern in Ghana due to its derived socio-economic benefits. "Reference [2] enumerated employment, ecotourism and major protein source as some of such benefits." Besides these benefits, the lake water is used for domestic purposes and has since served as the drinking water source to the people in the basin. However, the use of agrochemicals within the Lake Bosomtwe basin has been intensified within the last decade [3]. The agrochemicals have brought increased productivity and other benefits in terms of food security [4]. On the other hand, exposure to residues of the agrochemicals may affect the environment and human health through different emission routes [5]. The problems associated with fertilizer and pesticide use in the Lake Bosomtwe basin seem to carry with it a higher price, which, if not identified and checked, will overshadow the desired benefits [6] [7]. Pesticide and fertilizer residues carried into the lake water may potentially impair the quality of the lake water [8]. Mostly, the quality of the lake water in terms of its physico-chemical properties is often assessed to the exclusion of pesticides. This study was to assess pesticide and nutrient loads of the Lake Bosomtwe in the Ashanti Region of Ghana.

Study Area
The study was conducted in three communities that engaged in extensive farming along the banks of Lake Bosomtwe as shown in Figure 1. The Lake is located in the Bosomtwe-Atwima-Kwawoma District of the Ashanti Region of Ghana.
The District lies within latitude 6˚43' North and longitude 1˚46' West.
The Lake Bosomtwe area is located within the equatorial zone with a rainfall regime typical of the moist semi-deciduous forest zone of Ghana [9]. The lake almost covers all the flat-leveled low lands between the high lands of the Bosomtwe basin and the remaining little flat-leveled low lands of the basin are used by local inhabitants to carry out subsistence agriculture. Most of the farmers are also involved in other cash crop farming such as cocoa, oil palm and citrus plantations which are done on a relatively small scale [9].

Research Design
Field and laboratory techniques were used in this study. Purposive sampling technique was used to sample water from the selected communities for laboratory analysis. Fifty-four (54) lake water samples were collected from September,  loads. Samples were analyzed using the procedures prescribed by American Public Health Association [10] with minor modifications. A structured questionnaire was used to assess the level of use of pesticides and fertilizers by inhabitants within the Bosomtwe basin. Using discriminative snowball which is also non-probability sampling technique, sixty (60) respondents, twenty (20) from each community were selected for interview to take inventory of pesticides and fertilizers application in the basin.

Solid Phase Extraction and Elution of Pesticides
The water samples were filtered by passing each sample through a filter paper. A volume of 500 mL of each sample was extracted at room temperature using solid phase extraction method. A weak anion exchange solid extraction octadecyl C 18 cartridges were preconditioned with 5 mL of 0.1% NH 4 OH in methanol followed by double distilled water. Water samples were passed through C 18 column cartridges through polypropylene tubing under vacuum at a high flow rate (10 mL per minute). A volume of 2 mL of methanol was used to elute the uncategorized organic compounds into a sample valve. Each extract was then dried using The residue levels of the pesticides were quantitatively determined by the external standard method using peak area. Measurement was carried out within the linear range of the detector following the procedures described by [11] [12].
The peak areas whose retention times coincided with the standards were extrapolated on their corresponding calibration curves to obtain the concentration.
The limit of detection of the pesticides determined was based on the extract of the fortified samples that were serially diluted by a factor of two to give different concentrations. One out of each concentration that gave a response three times the standard deviation of the least fortified sample was noted tory, indicating a fairly good precision for most of the analytes. The limit of detection (LOD) (i.e., concentration that yielded signal to noise ratio of ≥3) and limit of quantification (LOQ) (i.e., concentration that yielded signal to noise ratio of ≥10) for the various analytes were determined for each sample and the median LOD and LOQ values were reported as the threshold values for each analyte.

Nutrient Loads of the Lake Water
Phosphate and Nitrate were the main nutrients whose loads were determined following the standard procedures prescribed by reference [10].

Data Analysis
The data obtained were analyzed using Statistical Product Service Solutions (SPSS version 20) for descriptive statistics and the results were presented as shown below. Table 1 shows the mean concentrations of pesticide loads of Lake Bosomtwe.  Dichlorvos recorded a mean concentration of 0.11 ± 0.09 ppb with minimum and maximum concentrations of 0.03 ppb and 0.18 ppb respectively. The concentration of dichlorvos was a bit lower when compared with the WHO/USEPA guidelines of 5 ppb for surface water. "Reference [13] attributed movement of contaminants into the lake Bosomtwe to farming activities occurring in the basin." According to [14], the toxicity of dichlorvos for freshwater and estuarine fish is moderate to high, and it does not bioaccumulate in fish. However, dichlorvos has the potential to induce altered immune response in fish [15].

Organophosphate Pesticides
Diazinon had a mean concentration of 0.28 ± 0.03 ppb during the study. cides have been extensively reported by [6] in Fosu lagoon, Chemu lagoon, Korle lagoon all in Ghana. Coumaphos has been linked to cause so many disturbances in aquatic systems particularly lakes [18]. An increasing number of studies linked exposure to TPhP with reproductive and developmental toxicity, neurotoxicity, metabolic disruption, endocrine effects, and genotoxicity. TPhP has also been found to induce significant estrogenic activity. Organophosphates have been identified to be a contributing factor of eutrophication in water bodies particularly lakes [19].

Organochlorine Pesticides (OC's)
Eight (8) problematic class of organochlorine pesticide residues were detected in the samples as shown in Table 1 Exposure to concentrations of organochlorine pesticides over a long period may eventually lead to a substantial body burden of toxic chemicals. Acute ingestion of aquatic products contaminated with organochlorine pesticides may cause a loss of sensation around the mouth; hypersensitivity to light, sound, and touch; dizziness, tremors, nausea, vomiting, nervousness, and confusion [20].
Population-based studies have revealed possible relations between the exposure to organochlorine pesticides and serious health effects including cardiovascular diseases, negative effects on the male reproductive system and on the nervous system, dementia, and also a possible increased risk for non-Hodgkin's lymphoma [21].

Synthetic Pyrethroids
Permetrin was the only pesticide identified under this group and a phenol type

Nitrate
The nitrate levels recorded during the study ranged from 0.01 mg/L to 0.25 mg/L with a mean value of 0.15 ± 0.05 mg/L as shown in Table 2. The mean nitrate value recorded for the study was a bit lower when compared with the overall mean nitrate concentration of 1.3 mg/L recorded by [13] for Lake Bosomtwe.
However, the concentration observed for this study (0.16 mg/L) by far fell in line with the nitrate levels obtained by [22] in Lake Volta (0. farmers. "Reference [13] attributed nitrate levels in surface water to increase in surface runoff, bare areas and leaching of nitrogenous fertilizers from nearby farmlands." A study by [24] concluded that, nitrogen fertilizer application contributed to an increase in nitrate levels in surface water through surface run-off.
Fertilizers on farmlands could be sub-lethal to native fish species and other aquatic organisms [25].

Phosphate
The phosphate level ranged between 0.098 mg/L to 0.68 mg/L with a mean concentration of 0.40 ± 0.12 mg/L as shown in Table 2. The mean concentration of phosphate had marginally increased when compared with the mean values of 0.40 mg/L recorded by [13] in the same lake. The mean phosphate concentration for this study was slightly higher when compared with the values (0.031 mg/L) recorded by [26] in the same lake. In view of this, lake can be said to be polluted considering the fact that the minimum phosphate level for most uncontaminated lakes ranges from 0.01 -0.03 mg/L [27]. The level of phosphate in the lake water  [28]. More so, the gradual increase in phosphate concentration in the lake water may be also attributed to the use of phosphate fertilizers, detergents and waste from domesticated animals around the lake. This is an indication of anthropogenic pollution [29]. "Reference [30] reported that high values of phosphate support algae growth and may affect the fish in the lake water."

Background Information about Farmers
The study revealed that majority of the respondents about 34% had no formal education and 43%, had basic education as shown in Figure 2. "Reference [13] enunciated that, the low level of education of the people in the Bosomtwe basin could also be an indicator of poor or misapplication of agrochemicals on farms." Misapplication of agrochemicals enhances movement of chemicals into water bodies causing a whole lot biological and chemical disturbances [31].
Furthermore, most of the farmers within the Bosomtwe basin were low income earners. 90% of the respondents earned between 100-300 Ghana Cedis within a month as shown in Figure 3. In view of this, there may be over dependence on the few resources available while the inhabitants quest to get means of subsistence. Often the problems of income earned and the environment are intertwined  and poverty varies proportionally to environmental degradation [32]. The World Bank maintains a notion that the poor do not willfully degrade the environment but poor communities often lack the resources to avoid degrading their environment [32]. The inhabitants within such communities therefore adopt poor low technological and ecologically threatening land use practices which significantly affects the lake water quality [33] [34].

Farmers' Knowledge of Pesticide
"Reference [35] posited that the manners in which pesticide products are used are likely to be driven by the extent of knowledge an individual has on the product." Pesticide labels though are contained in features that are known or easily comprehended and not too abstract to users [36], it was however revealed that 60% of the farmers were unable to read the manufacturer's instruction while 40% were able to read manufacturer's instructions. Meanwhile 53% of the total respondents that could read manufacturers instruction did not respect manufacturer's instruction. This may give satisfactory reasons for farmers' poor knowledge of the risks associated with the use of pesticides, including the essential role of the correct application and the necessary precautions [37]. Another study has reported that even farmers who can read the manufacturers' instructions are sometimes unable to translate this awareness into their practices [17] and this is not different from farmers within the Bosomtwe basin.

Farmers' Perception of Pesticide and Fertilizer Use
To find the extent of farmers' perception of pesticides and fertilizers use, it was divulged that 83% of the farmers within the Bosomtwe basin used pesticide and fertilizer in securing good crops while 13% did not use pesticides or fertilizer at all. The perception of the use of pesticides in the Bosomtwe basin was not different from the perception of most farmers in developing countries [15]. Farmers within the Bosomtwe basin see agrochemicals (pesticide and fertilizer) as a common element of agricultural technology and are commonly utilized throughout production seasons for controlling diseases, pests and weeds [38]. Farmers enumerated reasons for using agrochemicals which were in line with the claims of [39] which include economic benefits such as yield and quality of crops, decrease of other inputs like labor and fuel, etc.

Conclusion and Recommendation
The findings from the survey and laboratory results showed appreciable levels of pesticides and nutrients in the lake water. Most of the organochlorine pesticides detected in the lake water were not actively used in the basin anymore but their concentration still persists. The mean concentration of diazinon (0.28 ± 0.03 ppb) was higher than the WHO 0.05 ppb and USEPA 0.04 ppb for surface water bodies. The detection of diazinon confirms the findings from the field survey, which revealed that diazinon, is an active ingredient of a pesticide with a trade name "Akate suro", which is extensively used by cocoa farmers along the banks