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An evaluation of heavy metals concentration in the choba section of the new Calabar river, Eastern Niger Delta

Heavy metals are dangerous because they tend to accumulate. Compounds accumulate in living things any time they are taken up and stored faster than they are broken down or extracted (metabolized). Heavy metals can enter the water supply by industrial or consumer waste or even from acidic rain breaking down soils and releasing heavy metals into streams, lakes, rivers and ground waters.1 Although some heavy metals such as Manganese, iron, copper and zinc are essential micronutrients, other such as mercury, cadmium and lead are not required even in small amounts by any organisms.2 Some heavy metals become a matter of concern because of their toxicity and tendency to accumulation in food chains. Fishes, mollusk or another aquatic life are located at the end of food chain may accumulate metals and pass them to the human being through food causing chronic or acute diseases.3 Recent researchers have found that even low levels of mercury, cadmium, lead, aluminum and arsenic can cause a wide variety of health problems.


Introduction
Heavy metals are dangerous because they tend to accumulate. Compounds accumulate in living things any time they are taken up and stored faster than they are broken down or extracted (metabolized). Heavy metals can enter the water supply by industrial or consumer waste or even from acidic rain breaking down soils and releasing heavy metals into streams, lakes, rivers and ground waters. 1 Although some heavy metals such as Manganese, iron, copper and zinc are essential micronutrients, other such as mercury, cadmium and lead are not required even in small amounts by any organisms. 2 Some heavy metals become a matter of concern because of their toxicity and tendency to accumulation in food chains. Fishes, mollusk or another aquatic life are located at the end of food chain may accumulate metals and pass them to the human being through food causing chronic or acute diseases. 3 Recent researchers have found that even low levels of mercury, cadmium, lead, aluminum and arsenic can cause a wide variety of health problems.
Heavy metals toxins contribute to a variety of adverse health effects. These exit over than 20 different heavy metals toxins that have impacts on human health and each toxin will produce different behavioral physiological and cognitive changes in an exposed individuals. The degree to which a system organ tissue or cell is affected by a heavy metal toxin depends not only on the toxin its self but also on the individuals degree of exposure to the toxin. 4 The toxicity of heavy metals can be listed in order of decreasing toxicity as Hg>Cd>Cu>Zn>Ni>Pb>Cr>Al>Co, also this is only approximate as the vulnerability of species to individual metals varies. Toxicity also varies according to the environmental conditions that control the chemical speciation of metals.Because Water pollution is a significant problem and an essential natural resource for human life, there is need for assessment of the degree of contamination. More so, water is an important resource of developing economics and society in terms of agriculture, industry and various facilities. 5 Rivers not only supply water for human consumption but also receive wastewater discharge from all human activities. In the past two decades there have an increasing public awareness of the hazards exit from the contamination of the environment by toxic substances. Therefore in order to maintain the delicate relationship between human development and the quality of the environment, there is need for constant monitoring and evaluation of human activities in the Choba section of the New Calabar River that have the potential of altering the quality of the environment within which such activities occur. This is very necessary for risk assessment.

The study area
The New Calabar River and its tributaries are all located in Rivers State. It is a low lying deltaic river which rises at approximately latitude 5°10'N and longitudes 6°50'E near Elele-Alimini and flows Southward for roughly 150km before its discharge into the Atlantic Ocean at about latitudes 4°20'N and longitudes 7°00'E. 6 It occupies a low relief region, ranging from 0-50m above sea level at the low zone, to 50-100 above sea level at its source. The soil of the river basin consists of clays, silt and sand, with high organic matter. 7,8 The river is unidirectional in the upper reach and tidal in the lower reach. Its upstream reach is fresh water with tropical lowland, dense rainforest through secondary forest/farmland vegetation. The downstream reach is however brackish and consist of Mangrove swamp forest.
The Choba section of the New Calabar River is within Obio-Akpor Local Government Area alongside the Port Harcourt Local Government Area which forms the Port Harcourt Urban Area in Rivers State, Eastern Niger Delta, Nigeria. Rivers State is located in the South-South geopolitical zone of Nigeria and the eastern sector of the oil-rich Niger Delta region of the country. Port Harcourt doubles as the Capital City of Rivers State, and also the largest city in the State. The Port Harcourt urban area has a total population figure of 1,382,592. 9 Obio-Akpor Local Government Area is one of the eight (8) Local Government Areas that forms the Greater Port Harcourt urban area, namely: Port Harcourt, Okrika, Obio-Akpor, Ikwere, Oyigbo-Bolo, Tai and Eleme Local Government Areas respectively. As at 2012, the Greater Port Harcourt urban area had an estimated total population of 1,947,000 (Nigerian Administrative Division: City Population). This made it the 5th largest urban area in Nigeria; only after Lagos, Kano, Ibadan and Abuja. Port Harcourt has a tropical monsoon climate; having a lengthy and mostly heavy rainy seasons and very short dry seasons. December and January are the only months that truly qualify as dry season months, with December averaging 20mm of rain. The city's heaviest precipitation is usually recorded in the month of September (averaging 367m of rain). The average annual temperature value in the city is typically between 25°C-28°C. 10

Methods of study
Standard field sampling techniques were adopted for the sample collection exercise. The sampling exercise for the work was carried out on two different trips, which were weeks apart. The first sampling trip was aimed at obtaining sample from the effluent fallout point along the New Calabar River. The second sampling trip involved sampling both surface water and river sediment also along the New Calabar River. Due to the river in nature of the sampling locations, transportation from one location to the next was achieved by the use of a paddling boat. The sampling exercise for surface water and river sediment started off with sampling for river sediments first. This approach to sampling was adopted due to a time sensitive phenomena typical of that part of the New Calabar River. The New Calabar River, around the Choba bridge axis of the East-west road is usually in a regressive position at its banks in the early hours of the day. Towards noon, the level of water at the bank of the river starts rising, thereby flooding portions of its banks that were earlier exposed in the morning hours. As such, river sediment sampling at those sites were only possible in the early hours of the morning. Therefore, river sediment sampling was started with from take-off point (Choba Bridge, Eastwest Road), moving further towards and beyond the Dufil Prima Foods Plant. The sediments collected were a mixture of sandy, muddy and clayey sediments. It was at the farthest location of river sediment sampling that the surface water sampling was started with; moving upwards back towards the Choba Bridge, i.e. start-off point. Table  1 shows the coordinates and elevation of sampling locations while Figure 1 is Satellite imagery of study area.
The flow direction of the river influenced the decision to start sampling for surface water at the farthest location of sampling river sediment. The sampling of surface water from the farthest location, then moving up towards the take-off point ensures adherence to the best sampling technique for surface water. This choice ensured the movement of the boat while sampling was to guide against the flow direction of the river. This made sampling of surface water from an undisturbed flow, possible. Unstable parameters such as pH, temperature and electrical conductivity were determined in the field using pH meter, mercury thermometer and conductively meter respectively. Figure 2 shows the sampling locations. The locations of the boreholes were obtained with a handheld global positioning system (GPs). Figure 3 is the Site of first river sediment sampling while Figure 4 showed Fire ravaged vegetation in New Calabar River.

Calculation of Contamination Factor (CF); Pollution Load Index (PLI) and Geo-accumulation Index (I geo )
Contamination Factor (CF): Pollution Load Index (PLI): Where CF= Contamination Factor n= number of metals C background value = background value of metal An example of this type index is the pollution load index (PLI), which is based on the concentration factor (CF) of each metal. 5

Index of geo-accumulation
An index of geo-accumulation (I geo ) was originally defined by Müller, 12 in order to determine and define metal contamination in sediments, 13

Results and discussion
Because the quality of the surface water only gives the momentary quality of the environment, the quality of the river sediment which gives a more definite detail of the quality of the environment is of more importance in interpreting changes in the quality of the environment. Results from sampling and analysis of the river sediment and surface water shows that the chemistry of the two varies distinctly from one location to the other and that certain locations could have been sites of localised pollution (Table 4). Table 5 shows the Pollution Index (P I ) values of sampled surface water while Table 6 shows the contamination factor values for river sediments.
The heavy metal contamination factor in river sediments across all sampling locations were of low to moderate contamination levels. Majority of metals were however of moderate contamination factor levels. Based on the Pollution Load Index, all the sampled locations were found to be polluted; with locations 3 and 5 being the most polluted. Heavy metal concentrations in the surface water sample were objectionable when compared to the WHO 14 permissible limits for drinking water. Those heavy metals are a great concern for the quality of fish consumed from the river. The pH reading for all the surface water samples were also found to be acidic like those of the river sediments; having pH values ranging from 5.6 -6.2. Because the quality of the surface water only gives the momentary quality of the environment, the quality of the river sediment which gives a more definite detail of the quality of the environment is of more importance in interpreting changes in the quality of the environment. 15 Results from sampling and analysis of the river sediment and surface water shows that the chemistry of the two varies distinctly from one location to the other and that certain locations could have been sites of localized pollution.   Chromium (Cr) pollution levels were slightly insignificant in most of the sampling locations, except for locations 6 and 7 which had pollution index values 13 and 8.8 respectively. Of all the heavy metals, Lead (Pb) recorded the most chronic levels of pollution across all the sampling locations; having pollution index values ranging 10-211. Next to Lead (Pb), Zinc (Zn) also recorded the chronic levels of pollution; ranging 11.6-50.6. On the other hand, Iron (Fe) recorded the least levels of pollution of all the other heavy metals, across all the sampling locations; recording 1.3 as its highest pollution index value.
Cadmium (Cd) pollution index levels were insignificant in almost all the sampling locations; with locations 6 and 8 recording pollution index levels 10 and 26.6 respectively. Figure 5 shows heavy metals concentrations while Figure 6 is the plot of Iron (Fe) concentration in river sediments. Figure 7 shows Chromium (Cr) concentration plot in surface water and Figure 8 is the plot of Lead (Pb) concentration in surface water. Figure 9 is a plot of Cadmium (Cd) concentration in surface water while Figure 10 is Manganese (Mn) concentration plot in surface water.

Conclusion
The heavy metal contamination factor in river sediments across all sampling locations were of low to moderate contamination levels. Majority of metals were however of moderate contamination factor levels. Based on the Pollution Load Index, all the sampled locations were found to be polluted. Heavy metal concentrations in the surface water sample were objectionable when compared to the WHO 14 permissible limits for drinking water. Heavy metal concentrations in the surface water sample were objectionable when compared to the WHO permissible limits for drinking water. The pH reading for all the surface water samples were also found to be acidic like those of the river sediments with pH values ranging from 5.6 -6.2. Because the quality of the surface water only gives the momentary quality of the environment, the quality of the river sediment which gives a more definite detail of the quality of the environment is of more importance in interpreting changes in the quality of the environment. Results from sampling and analysis of the river sediment and surface water shows that the chemistry of the two varies distinctly from one location to the other and that certain locations could have been sites of localized pollution.
This study therefore provides a complete sight on pollution levels and risks presented by heavy metals in water and sediment and offer reasonable evidence on the greatest need to fully assess the risks of heavy metals and other pollutants to secure the health of the community. The awareness of risks assessment shall be a priority considering constant increase in heavy metal and general environmental pollution globally in water, air and sediment. The continuous and/or periodical acquisition of data on the quality of the water bodies is essential for sustainable management of risk. [17][18][19][20][21][22][23]