Irrigation water quality and its impact on the physicochemical and microbiological contamination of vegetables produced from market gardening: a case of the Vea Irrigation Dam, U.E.R., Ghana

The rationale for this study was to assess the physicochemical and bacteriological qualities of the Vea irrigation water and resultant effects on the quality of fresh vegetables produced in the area and associated implications for consumers ’ health. A total of 45 water samples were collected from the reservoir and canals. Also, 16 vegetable samples comprising four samples each of tomatoes, carrots, spring onions, and cabbages were collected from four farms with installed irrigation systems fed by the Vea Dam. The irrigation water samples were analyzed for total coliform (TC) and fecal coliform (FC), Escherichia coli , pH, and turbidity, while the samples of vegetables were analyzed for TC and FC, and E. coli. The results showed that except for pH, the bacterial loads and turbidity of the sampled vegetables and irrigation water were above the standards of the WHO and the International Commission on Microbiological Speci ﬁ cations for Food. Comparatively, the samples of cabbage recorded the highest levels of microbial contamination. The study suggests that the water should be treated before being used for irrigation; consumers should ensure that vegetables are properly washed and cooked/treated before consumption; and periodic monitoring and assessment should be done to ensure that the adverse effects of these activities are forestalled.


GRAPHICAL ABSTRACT INTRODUCTION
The scarcity of water has become a critical concern for global agriculture. It has become prudent that agricultural water users conserve water since agriculture continuously competes for limited water supply that is becoming scarcer.
One method of combating food insecurity and water scarcity is irrigation (Ding ). Irrigation is globally essential (Howell ). According to Jensen (), population increase puts pressure on irrigation systems. From canals, wells, and dams, water is made available to support households and livestock, as well as for irrigation purposes.
However, a challenging factor in the potential health hazards emanating from the usage of open water sources for the production of vegetables due to contamination cannot be underestimated (World Commission on Dams (WCD) ; United Nations ). Therefore, in lowincome countries, including Ghana, untreated wastewater is predominantly used for farming (Scott et al. ).
According to Westcot (), in commercial and smallscale farming, streams, lakes, groundwater, and dams, which do not meet the desired standards of irrigation, are predominantly used. Studies by Keraita & Drechsel () and Scott et al. () revealed that in certain cases, wastewater is deliberately used for irrigation because it is cheaper and provides organic nutrients. However, the associated environmental and health risks are ignored.
The microbiological characteristics of irrigation water are prudent predominantly because water polluted with excreta can introduce pathogens into farm products (FDA/ CFSAN ). The enteric bacterial load of fresh vegetables is an important concern for all patrons in the food industry, both locally and globally (Chang & Fang ). However, according to Scott et al. (), developing countries are unable to effectively treat wastewater before disposal. Therefore, large volumes of wastewater get into natural water systems, which are further used for irrigation.
In Ghana, a study carried out between 2007 and 2008 by the Small Grants Programme (SGP) of the UNDP/ GLOBAL Environmental Facility (GEF) discovered that vegetables consumed in Accra had additional dozens of chemicals and fecal coliform (FC) above permissive limits.
Less than 10% of urban dwellers have access to proper water systems. Thus, wastewater is channeled from gutters to larger drains and streams for irrigation (Keraita et al. ). In some instances, low-quality water from drains, shallow wells, and streams is used (Amoah et al. ).
According to Keraita & Drechsel (), in Ghana, there is a high demand for fresh produce (vegetables). For instance, though fresh salad is not a major component of Ghanaian diets, in recent times, it has become a common supplement in fast foods. This is predominately due to the awareness of its health benefits (Heaton &  plements daily. This study was, therefore, conducted to assess the irrigation water quality (physicochemical and microbiological properties) of the Vea Dam, and its impacts on the quality of the vegetables produced from market gardening, and consumer health. The research also evaluated the effects of the irrigation water quality on the health risks that the people and the livestock that resort to using the dam as a source of drinking water are exposed to.

Description of the study area
The Vea irrigation project is one of the strategic investments in the Upper East Region of Ghana. It is a multipurpose project that supports crop, fish, and livestock production, as well as domestic purposes. The Vea Dam is located in the Bongo District between latitudes 10 48 0 and 10 56 0 north and longitudes 0 44 0 and 0 56 0 west ( Figure 1). It shares boundaries with Balungu, Zaare, Gowrie, and Vea townships to the north, south, east, and west, respectively (GSS ). The area forms part of the Guinea Savannah Woodland, which is characterized by a single maximum rainfall ranging between 600 and 1,400 mm (Ampadu et al. b).
The focus of the Vea Irrigation Dam was to enhance food production and economic standards through crop production, animal rearing, fishing, and agroforestry. The dam is also a source of drinking water to some areas within the

Sampling site
The research was conducted within the Vea catchment, specifically on the Vea Dam, Nyariga canal, and four vegetable farms irrigated with water from the canal.
Vegetables comprising tomato, cabbage, spring onion, and carrot were collected for microbial analyses. A preliminary visit to the study area in the form of a reconnaissance survey was carried out to, among other things, determine the various vegetables cultivated within the catchment.

Sample collection
The catchment was divided into three grids/zones, i.e. the upstream, the middle stream, and the downstream using ArcGIS 9.3©. Within each subdivision, three locations were identified at the entry, middle, and exit points of the subdivision. Three water samples (500 ml each) were collected from these locations at a depth of 5 cm below the surface of the

Bacteriological method
The membrane filtration technique was employed to determine TC, FC, E. coli, and Salmonella. Bacteriological parameters were determined by filtering 100 ml of the water samples through 0.45 μm pore-size cellulose membrane filters. The membrane filters were then plated on media for faecal coliform (mFC) agar and incubated at 44 ± 2 C for 18-24 h for FC, m-Endo, and Salmonella-Shigella agar media at an incubated temperature of 37 ± 2 C for 18-24 h to enumerate TC and Salmonella, respectively (APHA ), while membrane infiltrating (MI) agar media at an incubated temperature of 35 ± 0.5 C for 24 h were used for E. coli (USEPA ).

Determination of physicochemical parameters
The pH and the turbidity of the water samples were also determined. The pH was measured with a 211 Chip pH meter (Hanna Instruments Inc., Woonsocket, R1, USA), whereas turbidity was determined using an H1 93703 Microprocessor turbidity meter.

Analysis of data
The descriptive statistics were computed using Microsoft Excel 2016 version. The enteric bacteria loads of TC, FC, and E. coli (CFU/100 ml) were normalized by log transformation for the analysis of variance using the Microsoft Excel 2016 version and R software. The significance level (oneway ANOVA) of the analyzed results was quoted at P < 0.05. An empirical orthogonal function (EOF) was done on the obtained data and the cumulative proportions were used in the interpretation of the results, whereas the interrelationships of the variables were determined using covariance-variance analysis. pH and turbidity were not considered in the EOF and covariance-variance analysis since they were not included in the assessment of vegetable quality.

RESULTS
The bacteriological quality of water samples Table 1 and Figure 3 present the summarized results of the enteric bacterial load of the irrigation water from the reservoir and the canal. The results of the water samples from the dam showed that the population of TC ranged between 3.56 and 3.98 (log CFU/100 ml), while the FC results ranged from 3.20 to 3.96 (log CFU/100 ml). The results of E. coli analysis ranged between 3.00 and 3.95 (log CFU/     The bacteriological quality of vegetable samples   Physicochemical properties of the irrigation water Table 3 and Figure 5 show the physicochemical properties of the water samples taken from the dam and the irrigation canal. The turbidity of the dam and the canal ranged from 71 to 103 Nephelometric Turbidity Units (NTUs) and 75 to 110 NTUs, respectively. Also, the pH of the water sampled from the dam and the canal ranged from 7.56 to 8.42 for the former and from 6.96 to 7.85 for the latter.

Variance-covariance matrix and EOF
The results for the computed correlation analysis showed that except for FC and TC that showed a negative associ-

Properties of the irrigation water and vegetables
The microbial value of irrigation water is vital to the safety of fresh and minimally handled vegetables (Bihn & Gravani ). Table 1   revealed that sanitation was poor within the area of study.
Open defecation and improper waste disposal were studied and these were said to have affected the quality of the irrigation water. Runoffs from defecation sites were observed to find their way into the main river channel. Also, animal rearers were observed using the dam as a source of water for their livestock, especially cattle. Since animal droppings have been found to negatively impact water quality, depos-

Physicochemical properties of irrigation water
pH is the degree of acidity or alkalinity of an aqueous solution. The WHO recommends a pH value between 6.5 and 8.5 for human consumption of water. According to the results shown in

CONCLUSIONS
The poor water quality in the irrigable water can be attributed to human-inducing activities, including the application of manure as a cheap but potent source of fertilizer, the