Surface water samples were collected from Santa Barbara River using sterilized glass bottles—upstream and downstream on the Santa Barbara River. Samples were collected upstream from station 1 to 4 at intervals of 200 meters and then from station 5 to 9 with varying distances downstream, upstream and control point. Immediately after the collection of each sample, sample bottles were appropriately labeled and immediately stored in an ice chest. The samples were thereafter transported to the laboratory within 24 hours for analysis. Sample

storage was carried out according to standard laboratory practices as recommended by the American Public Health Association [14] . A total of one hundred and twenty (120) water samples in four replicates from 10 sample stations and from a control point were analyzed for the physiochemical parameters that were geo-referenced using a handheld Global Positioning System (GPS).

The physical and chemical parameters analyzed are temperature, (pH), electrical conductivity, salinity, TDS, DO, and BOD. The methods used are as described by [14] .

Turbdity

Test Method: Nephelometric Method

Standard Reference: APHA 2130B: Apparatus used: HACH 2100P Turbidimeter

Calculation:

Nephelometricturbidityunits ( NTU ) = A × ( B + C ) C

where A = NTU found in the diluted ample;

B = Volume of dilution water, ml;

C = sample volume taken for dilution, ml.

TDS

Test Method: Total Dissolved Solids; Dried At 180˚C (Gravimetric Method)

Standard Reference: Apha 2540 C

Calculation:

TotalDissolvedsolids ( mg / L ) = ( W 1 − W 2 ) × 1000 Samplevolume ( ml )

where:

W₁ = Weight of dried residue + dish;

W₂ = Weight of empty dish.

Total Suspended Solids (TSS)

Test Method: Total Suspended Solids Dried at 103˚C - 105˚C (Gravimetric method)

Standard Reference: APHA 2540 D

Calculation:

TotalSuspendedsolids ( mg / L ) = ( W 1 − W 2 ) × 1000 Samplevolume ( ml )

where:

w₁ = Weight of dried residue + dish;

w₂ = Weight of empty dish.

Alkalinity

Test Method: - Titrimetric method

Standard Reference: - APHA 2320B

Calculation:

Phenolphthalein   Alkalinity ,   as   mgCaCO 3 / L = A × N × 50000 mlsample

where:

A = mL of standard acid used;

N = normality of standard acid.

Total Alkalinity

Phenolphthalein   Alkalinity ,   as   mgCaCO 3 / L = B × N × 50000 mlsample

where:

B = total mL of titrant used to methyl orange or bromcresol green end point;

N = normality of standard acid.

Hardness

Standard Reference: APHA 2340C

Method: EDTA Titrimetric method

Calculation:

Hardness ( EDTA )   as   mg   CaCO 3 / L = A × B × 1000 mLsample

where:

A = mL titration for sample and;

B = mg CaCO₃ equivalent to 1.00 mL EDTA titrant.

Calcium

Standard Reference: APHA 3500-Ca-B

Method: EDTA Titrimetric method.

Calculation:

mg   Ca / L = A × B × 400.8 mLsample

Calciumhardnessas   mg   CaCO 3 / L = A × B × 1000 mLsample

where:

A = mL titrant for sample and;

B = mg CaCO₃ equivalent to 1.00 mL EDTA titrant at the calcium indicator end Point.

Magnesium

Standard Reference: APHA 3500-Mg-B

Method: Calculation from total hardness and calcium.

Calculation:

mg mg/L = [total hardness (as mg CaCO₃/L) − calcium hardness (as mg CaCO₃/L)] × 0.243

Biological Oxygen Demand (BOD₅)

Standard Reference: APHA 5210 B

Test Method: 5-Day BOD Test.

Calculation:

BOD₅ (mg/L) = [DO1 − DO0]/B

where:

DO0 = initial dissolved oxygen (immediately after preparation);

DO1 = final dissolved oxygen (after 5 days of incubation);

B = Fraction of sample used.

Chemical Oxygen Demand

Standard Reference: APHA 5220 C

Test Method: Closed Reflux—Titrimetric method.

Calculation

COD ( mg / l ,   as   O 2 ) = ( BlankTiter − SampleTiter ) × MolarityofFAS × 8000 SampleVolume

where:

A = mL FAS used for blank;

B = mL FAS used for sample;

M = molarity of FAS, and;

8000 = milli equivalent weight of oxygen × 1000 mL/L.

Chloride

Test Method: Argentometric Titrimetric Method

Standard Reference: APHA 4500 Cl⁻ - B

Calculation:

mg   Cl − / L = ( A − B ) × N × 35450 mLsample

where:

A = mL titration for sample;

B = mL titration for blank;

N = normality of AgNO₃.

Standard Reference: APHA 3111B

Test Method: Air-acetylene Flame Atomic Absorption Spectroscopy Method. The Air-acetylene Flame Atomic Absorption Spectroscopy Method was used for heavy metal determination. Calibration analysis was carried out by diluting 1000 ppm stock solution of the individual elements (Pb, Fe, Cu, Zn, Ni, Co and Mn) while three standard working solutions were prepared from the stocks (ranging from 0.1 mg/L - 10 mg/L).

The physicochemical parameters comprise pH, Electrical conductivity, TDS, salinity, turbidity, DO, COD, BOD.

pH: The surface water pH of Santa a River ranged between 6.90 and 7.50 across the sampling stations. The results show the water is slightly acidic to alkaline. The pH values observed in the study falls within the acceptable range for pH which ranges (6.5 - 8.5) in line with WHO Standards [15] (WHO, 2011A). However, the result shows the presence of pollutants from the hydrocarbon spill entering surface water and creating an imbalance in the pH of aquatic ecosystem, such that it fluctuates below and above the normal value of 7.

Electrical Conductivity: The mean electrical conductivity values recorded across the stations varied from 19739.41 ± 273.04 µS/cm to 28920.64 ± 290.83 µS/cm (Figure 2). The obtained electrical conductivity indicates brackish water. Conductivity varies according to season according to [16] - [21] . The results of electrical conductivity across the stations exceeded the WHO limit of 2500 µS/cm [22] . High values of electrical conductivity recorded in the Santa Babra River indicate the presence of dissolved substances, chemicals and minerals released from oil spillage. This shows a strong correlation between TDS and cations which is responsible for the high electrical conductivity observed across all sampled stations.

TDS: The mean TDS values ranged 10472.72 ± 1034.95 mg/l - 16538.19 ± 1253.63 mg/l across the stations. The maximum permissible value of 1000 mg/l for TDS was exceeded in all the stations [23] . The result of TDS was below the range of 1235 - 19846 mg/l reported for brackish Elechi Creek in Port-Harcourt Nigeria [8] . All values recorded were above the acceptable limits. The TDS is related to the electrical conductivity and salinity of the water. The high TDS values in this study is attributed the hydrocarbon spill contamination.

Salinity: The results of salinity recorded across stations was 13.29 ± 0.72 ppt - 17.30 ± 1.24^a ppt. Salinity was low for all the sampling stations and the maximum permissible limit of 200 g/l was not exceeded. Changes in salinity are the direct cause of some species disappearing and others occurring [24] . Variations in salinity can also contribute indirectly to food shortages and, consequently, they impact zooplankton abundance [25] .

Turbidity: Turbidity ranged 7.10 - 37.48 NTU with mean varying significantly from 2.53 ± 0.46 to 35.42 ± 5.63 NTU across the stations (Figure 2). The WHO limit of 5 NTU for turbidity was exceeded across the stations for surface water samples analyzed ([23and [15] ). At P < 0.05 level of significance, this research observed significant difference in turbidity across the station for surface water. The high turbidity could be attributed to the discharge of crude oil waste or bunkering activities within the study area. [26] reported turbidities in natural waters rarely surpass 20000 mg/l and even muddy waters usually have less than 2000 mg/l. The observed turbidity level in the study area is within 2 NTU - 47 NTU for the turbidity of Nigerian water bodies [27] . High turbidity waters have been linked to microbial contamination [28] .

DO: The DO across the stations ranged 6.21 mg/l - 7.371 mg/l. Elevated oxygen levels in surface water range from 6.3 - 8.3 mg/l [29] . The acceptable value of 5 mg/l was exceeded in all the stations for surface water samples thereby making the water oxygenated sufficiently to sustain aquatic life. Similarly, the dissolved oxygen level in the Santa Barbara River exceeded the maximum permissible limit of 6 mg/l [15] [23] . DO is a useful indicator of water quality, ecological standing, efficiency, and health of a river [30] . [31] recorded higher values of DO early rainy season compared to dry season because increased rainfall and river runoffs result to increase in water current flow and high mixing rate. The concentration of DO in aquatic environment at any point in time is influenced by the biological activity of flora and fauna, BOD degradation process, sediment oxygen demand and oxidation process [32] and [33] . Temperature and salinity also affect solubility and availability of oxygen in aquatic environment. [34] [35] argued that solubility of oxygen decreases as temperature and salinity increase and is more dependent on temperature variation than on salinity variation.

Chemical Oxygen Demand (COD): The COD across the stations ranged 49.72 mg/l - 90.03 mg/l. According to [36] COD is an important index for evaluating of water pollution. COD provides information about the readily oxidized fraction of the organic load or reduced compounds in waters, indicating the degree of water pollution [37] .

Biological Oxygen Demand (BOD): The BOD varies from 1.11 mg/l - 2.71 mg/l across the stations. The maximum permissible value of 1.9 mg/l for BOD was exceeded in the study area [23] . High values of BOD signify high concentrations of organic contaminants and relatively high biological activities (microbial and faunal activities) resulting in the reduction of oxygen content in the water body. Unpolluted waters typically have BOD values of 2 mg·L⁻¹ or less, whereas water bodies receiving wastewater may have BOD values up to 10 mg·L⁻¹ or more at proximities to discharge points [38] . According to [39] BOD values 2 mg/l - 4 mg/l indicate unpolluted whereas those above 5 mg/L are indicative of severe pollution. This result suggests the surfactants used after the hydrocarbon pollution was effective.

Temperature: Temperature ranged 28.04˚C - 31.79˚C across stations. The observed temperature values in the area are in agreement with that of the Niger Delta. [39] reported temperature ranges of 25˚C - 35˚C. The temperature of this current research agrees with previous works carried out in the Niger Delta [40] [41] and [42] . Temperature fluctuations occur seasonally often higher in the dry season months compared to wet season months, typical of tropical African inland water systems [43] . Seasonal variations in water temperature suggest surface water temperatures closely follow ambient air temperature [44] also temperature is inversely proportional to DO [45] .

Alkalinity: The total alkalinity across the stations was 43.95 mg/L - 73.87 mg/L and the measured values were below the WHO limit of 120 mg/L. Alkalinity is the water’s ability to resist changes in pH and is a measure of the total concentration of bases including carbonates, bicarbonates, hydroxides, phosphates, and borates [46] . Reactions between bases and neutralize acids, buffers changes in pH of aquatic media [46] . Higher alkalinity levels in surface water cushions acid rain effects and other acidic wastes thereby preventing pH changes that are harmful to aquatic life.

Total Hardness: The values of total hardness concentrations recorded in the water samples across the stations in the study area ranged between 794.80 mg/L and 1129.32 mg/L (Figure 3). Total hardness concentrations observed in the study were above the maximum allowable limit of 300 mg/L by WHO for fresh and portable water [47] . The total hardness also exceeded WHO revised maximum permissible limit of 500 mg/l [15] . Hardness of water may be caused by the occurrence of dissolved polyvalent metallic ions, mostly calcium ions (Ca²⁺) and magnesium ions (Mg²⁺).

TSS: The TSS concentrations ranged 1.33 mh/l - 5.13 mg/l. It was observed that the levels of TSS in the sample points were below 50 mg/L WHO limit for the protection of fisheries and aquatic life [48] . TSS in water is detrimental since they decrease water transparency, inhibit photosynthesis, increase sediments, smoothen breeding bed of aquatic organisms and eventually lead to an increase in sediments which contributes to the decrease in water depth [49] .

Anions: The concentration of phosphates ranged 0.06 - 0.07 mg/l. The sources of phosphates in surface and groundwater vary and may include atmospheric deposition, natural decomposition of rocks and minerals, weathering of soluble inorganic materials, decaying biomass, runoff, and sedimentation [50] . Excess phosphorus in water is considered a pollutant [51] and may be due to enrichment from allochthonous phosphorus-containing substances rather than oil exploration and production activities [52] . Chloride concentrations ranged 6019 mg/l - 9274.82 mg/l. Brackish waters often have chloride concentrations ranging from 500 - 5000 mg/l [53] . According to the [54] the use of road salt (sodium chloride) for deicing in road construction is a major man-made source for surface and groundwater. Run off during rains and storms aids in cycling road salt to rivers streams and groundwater reservoirs. The high chloride levels in the Santa Barbara River Nembe may be due to its unique estuarine environment where it mixes with salt water from the Atlantic Ocean. The WHO limit for chloride is 250 mg/l and chloride in the study area exceeds 250 mg/l however high chloride content is not known to cause any health risk or hazard. Fluoride levels in the Santa Barbara River Nembe ranged from 0.03 mg/l - 0.10 mg/l and were below the WHO limit of 1.5 mg/l for domestic purposes [55] . Fluoride concentrations in fresh water may be less than 1.0 mg/l and in natural waters its concentrations may exceed 50.0 mg/l [56] . The concentration of nitrates ranged from 1.7 mg/l - 1.6 mg/l. Nitrates are available in the aquatic system because of run off, dissolution of nitrogen rich geological deposits, N² fixation of cyanobacteria and biodegradation of organic matter [57] and [58] .

Cations: The concentration of calcium ion level 375.68 mg/l - 536.72 mg/l. Calcium ion is a metallic cation often present in fresh surface water bodies [59] . Cation concentration for sodium and potassium in Osioma River ranged from 1.35 mg/l - 1.43 mg/l and mean 0.25 mg/l respectively [60] . Magnesium ion levels ranged 88.35 mg/l - 243.24 mg/l. The values of calcium and magnesium ions recorded in the study indicated that all the samples were above the acceptable limits (50 mg/l) for human consumption [61] . Sodium ion concentration in the sampled river system was relatively high but varied from 1833 - 2755 mg/l across the stations. Increase in sodium ion concentration has been linked to crude oil leakage [62] . The potassium ion level across the stations ranged between; 41.27 - 121.17 mg/l across stations. Potassium ion was above the WHO limit.

Average arsenic concentration across all sampled stations was 0.001 mg/l (Figure 4). Arsenic concentration in the study area is below the WHO limit of 0.01 mg/l [22] for drinking water. High levels of arsenic in environmental media are of great concern as it is linked to adverse health issues. Several studies suggest a strong association between arsenic exposure and increased risks of both carcinogenic and systemic health risks [63] . The average concentration of cadmium was 0.001 mg/l across all the sampled stations and below the WHO acceptable limit of 0.01 mg/l [15] . The cadmium levels in the surface water in Santa Barbara River presents no danger or health concern as the background levels are below acceptable limits. Cadmium is present in the environment at low concentrations and increased levels linked to anthropogenic activities [64] . High cadmium levels in the environment are of global concern because of adverse effects resulting from human exposure, flora, and fauna. Major anthropogenic sources of cadmium are mining and smelting as well as refining of non-ferrous metal [65] other sources include fossil combustion and incineration of cadmium batteries in addition to plastics ( [66] [67] ). Studies suggest cadmium exerts toxic effects on the kidney, the skeletal system and the respiratory system and is classified as a human carcinogen ( [68] [69] [70] [71] ). Lead concentration across all stations was 0.001 mg/l. The lead levels in the surface water samples analyzed were lower than the WHO acceptable limit of 0.01 mg/l. Lead levels in the Santa Babra River Nembe are low and present no health effect or impact. The impact of lead in the environment is well known. Anthropogenic activities accounts for extensive environmental contamination from lead globally particularly mining, smelting, manufacturing, and recycling activities and use in a wide range of products [72] . Lead exposure accounts for 21.7 million persons having disability and death globally due to long-term effects on their health, with 30% idiopathic intellectual disability, 4.6% cardiovascular disease and 3% chronic kidney diseases [70] . The concentration of copper ranged from 0.03 mg/l - 0.07 mg/l while the mean concentration of copper was below 2 mg/l [73] . The concentration of zinc ranged from 0.08 - 0.16 mg/l while the average zinc levels were below 3 mg/l [71] . The low levels of heavy metal observed suggest the surface water in not polluted and the initial clean-up was effective. In the Niger Delta low heavy metal accumulation has been reported in Elechi Creek and Lower Bonny River, Benin River ( [8] [9] ). When anthropogenic activities increase significantly heavy metal contamination in the environment it causes harm to living organisms [10] . Toxicity of heavy metals occur when the rate of uptake exceeds the rates of physiological or biochemical detoxification and excretion [11] . Heavy metals are high priority pollutants because of their relatively high toxic and persistent nature in the environment [12] . Thus, heavy metals may be used as indicators of pollution in the study area.

Results of the TPH, PAH and BTEX concentration s in the study area shows that the TPH concentration ranged 0.37 - 1.41 g/L (Figure 6) while the average level of TPH in surface water from this study is 1.41 µg/L (Figure 5). The highest concentration was observed at station 9 BA/SW9 which had 1.41, followed by SUN/SW4 with 1.23 and the least was recorded at the control station. The result shows a significant difference (P < 0.05) across the sample stations. Higher concentrations of TPH were observed in areas that were more severely impacted that others within the study area. There was a decrease in trend in TPH a distance further downstream from the hydrocarbon spill site. There was spatial variation in the distribution of TPH across sampled stations. The spatial variation in the distribution of TPH across sampled stations suggests introduction of petroleum hydrocarbons to the study was because of the Santa Barbara hydrocarbon spill incident resulting in high level of petroleum hydrocarbons. The total mean concentration of TPH from all sample stations were lower than the [74] acceptable standard limit for petroleum hydrocarbons (300 μg/L) in river and basin water. Although clean-up activities were carried out remedial levels of hydrocarbons were detected in the analyzed sample. Inappropriate clean-up of hydrocarbon spill sites accounts for the higher concentration of TPH in sampling stations in the study area. According to [75] TPH of 168.33 µg/L was recorded in the Qua Iboe River Ibeno Akwa Ibom when hydrocarbon was spilled. Polluted sites with higher TPH levels of 73500 µg/l have recorded in surface water of Ubeji Riverin Warri, Niger Delta [76] . The total mean concentration of TPH from all sampled stations were lower than the [72] acceptable standard limit for petroleum hydrocarbons (300 μg/L) in rivers and basin water. The average level of TPH in surface water from this research is 1.41 µg/L which is significantly lower (P < 0.05) compared to values reported in other Niger Delta regions. The results for the PAH and BTEX show both values are <0.001 which is below the maximum contaminant level of 5 ppb for drinking water set by the [72] [77] and PAH was not observed in the surface water. The results suggest that the clean-up activities carried out on remedial levels of hydrocarbons were successful.

Microbial Population: The Total Heterotrophic Bacteria (THB) ranged from 2.58 CFU/ml to 6.17 CFU/ml (Figure 6). Total Heterotrophic Fungi population (THF) ranged from 2.59 CFU/ml to 4.17 CFU/ml. Hydrocarbon Utilizing Bacteria (HUB) population ranged between 0.24 CFU/ml and 1.27 CFU/ml. Hydrocarbon Utilizing Fungi (HUF) ranged between 0.16 CFU/ml to 1.01 CFU/ml. The result shows that the quality of surface water deteriorated because of bacterial population. The maximum permissible value of total coliforms in drinking water is 1 per 100 ml [78] and 10 per 100 ml [79] . The surface water is highly contaminated and portends potential public health hazards. The bacterial contamination in the surface water may be due to hydrocarbon spillage and sewage disposal as well as indiscriminate defecation into the water way [80] (see Figure 7).