This study was conducted to determine the levels of heavy metals in drinking water sources of Chingola District. The study also aimed at assessing variations in concentrations of each heavy metal in water with respect to different sources and season.
Arsenic levels were found to be beyond permissible levels in all ground water sources during the wet season both rural and urban. For Tap water, only three (3) sampling locations out of ten (10) had arsenic levels beyond permissible levels. UNICEF reported that the primary source of arsenic contamination in the populace is ground water sources (14). Reported elevated levels of arsenic during the wet season in this study agree with a number of studies conducted in other settings. However, very little information is available on heavy metal levels in drinking water sources in Zambia. Most available information on heavy metals in Zambia has to do with water samples collected from the soils and rivers especially Kafue River. Previous studies reported that Sediments Arsenic levels surpassed United States Environmental Protection Agency (USEPA) along Kafue River (15). Other studies also reported high levels of Arsenic groundwater and well water in the Mekong River basin of Cambodia (16). Similar to findings in this study; other studies also reported higher levels of arsenic during the wet season (17). This suggests that arsenic might be desorbed and leached from contaminated soils into shallow groundwater (18).
Observed fluctuations of arsenic are primarily induced by seasonally occurring groundwater movement (19). Elevated levels of arsenic may also be influenced by the weathering/erosion of minerals as well as application of various agricultural fertilizers (20, 21). Other studies reported that the presence of arsenic may also be attributed to anthropogenic activities, such as the use of herbicides (22). This means that water may get contaminated through improperly disposed arsenical chemicals and use of arsenical pesticides (23). It’s probable that apart from the natural and weathering processes of arsenic, use of agricultural pesticides/herbicides might contribute to the high levels of arsenic in ground water sources since small scale farming is the predominant activity in Chingola district especially rural communities.
Elevated lead beyond permissible levels was detected in a number of water samples in both dry and wet season. The highest median value was 0.025 for rural ground water sources during dry season. Previous studies in Nigeria revealed elevated levels of lead above permissible levels in various water samples (24, 25, 26). This study however, reported relatively higher concentrations of lead in the dry season than wet season contrary to findings by other studies which reported relatively higher concentrations of lead in the wet season compared to the dry season in ground water sources (27). Various factors are associated with increased levels of lead in drinking water sources. In this study, rural ground water samples reported relatively higher concentrations of lead compared to urban ground water sources and Tap water especially in the dry season. Khan et al. (28) identified improper disposal of sewage and solid wastes, over application of agrochemicals (pesticides and fertilizers), deteriorating condition of piping network and transportation as the major sources responsible for contamination of drinking water with lead. Agricultural activities may be implicated as the main source of elevated levels of heavy metals in water. Previous use of lead paints and leaded fuel may also be implicated since heavy metals are non-biodegrable and remain in the environment for a long time.
Manganese was detected from almost all the sampling locations in both dry and wet season. Only two sampling locations in the wet season reported concentrations below detection limit. The median concentration for Tap water and urban ground water sources during wet season exceeded ZABS permissible values of drinking water. Median concentrations for Tap water sources during dry season exceeded ZABS permissible values of drinking water. Similar study in past studies in groundwater and well water in the Mekong River basin of Cambodia reported high levels of Manganese (29). Equally, Buschmann et al. (30) reported higher concentrations of Manganese in wells. Manganese naturally occurs in many surface and ground water sources and in soils that may erode into these waters (31) however, past mining activities has been implicated to be responsible for elevated levels in drinking water sources in some studies (32).
Nickel concentrations exceeded WHO permissible levels in dry season in all water sources. The highest median concentration was 0.045 mg/l in Tap water during the dry season while the lowest median concentration was 0.006 mg/l in rural ground water sources during the wet season. Little information is available in Zambia on nickel levels in drinking water sources. Most information available is on studies which focused on river and soil samples. All studies on Zambia reviewed by the researcher did not report any significant amount of Nickel in water. However, studies in other settings have reported elevated nickel levels in drinking water sources. A study in Nigeria reported elevated nickel concentrations among other heavy metals in Bore-hole water from Kebbi state (33). Another study in Izmir, Turkey reported high levels of nickel beyond their safe limits in drinking water (34). Equally, a study in Greece, revealed high levels of nickel in drinking water from various regions of Greece (35). The European Food Safety Authority (EFSA) reported that nickel is a widespread component of Earth’s surface found in all environmental compartments and is ubiquitous in the biosphere (36). Weathering of rocks and soils has been identified as one of the main natural sources of nickel (37).
The median concentrations of iron in rural ground water sources for both dry and wet season exceeded permissible levels as provided by US EPA and EU. Previous studies elsewhere also reported that iron exceeded their respective permissible limits set by different organizations in some locations (38). Iron is frequently found in groundwater due to large deposits in the earth’s surface (39). The levels of iron in groundwater can be increased by dissolution of ferrous borehole and hand pump components (40). The use of groundwater for drinking is in many cases limited by the presence of dissolved iron. Iron gives the water an unpleasant metallic taste, and stain food, sanitary wares and laundry.
Median concentrations for the other heavy metals were below their respective permissible values. However, some of the sampling points reported values beyond permissible values for copper, cobalt and zinc. Concentrations of chromium and cadmium were below detection limits
A study by Ndilila et al revealed significantly higher Toenail concentrations of cobalt, copper, lead and zinc in the mining area compared to non-mining areas in Zambia (41). Others reported elevated cobalt and copper levels along Kafue River in Chingola district which he attributed to mining activities (42). Other past findings further found out that areas geographically distant from mining beds had only moderate or low heavy metal concentrations. Sampling locations with higher levels of zinc were rural ground water sources. Anthropogenic activities may be responsible for these elevated of zinc in some rural ground sources (43).
Cadmium and chromium were all below detection limit in the water sources for both wet and dry season of the study area. This implies that the study area had no traces of the metal ions being mentioned, or that their concentrations were just too low to be detected by the instrument of analysis. This is good news, since cadmium and chromium might be considered a threat according World Health Organization (44). The non-detect result for chromium in this study is an indication and likely confirmation of the absence of industrial activities which involves chromium and cadmium in its operations.
In this study; iron, arsenic, copper manganese showed a significant difference (P < 0.05) with respect to the three different sources of drinking water. Levels of arsenic, nickel, manganese and cobalt differed significantly between dry and wet season. Previous studies in Nigeria and Jordan also revealed significant (p < 0.05) heavy metal variation in terms of water source (45, 46).
This shows that different sampling locations contribute differently to the median heavy metal concentrations from various sources. This means that heavy metal contamination is likely to be anthropogenic. This result may be explained by the fact that such heavy metals which arise from anthropogenic sources are collected and concentrated during no-rain months, and then washed at the beginning of rainfall with the rain runoff and leached to the ground- water through soil (47). Variations in this regard may probably arise from changes along the groundwater flow path, and slight variations in net effect of the pH dependent processes of minerals dissolution and precipitations (hydrogeology) (48, 49).