Environmental Impacts Assessment of Shipping Activities on Water Quality of Apapa Bay, Lagos, Nigeria

doi:10.21203/rs.3.rs-3897858/v1

Activities at seaports could contribute to ecological hazards such as water pollution. In this study, the environmental impacts of shipping activities at Apapa Bay, Lagos, Nigeria, in relation to the water's physicochemical and potentially toxic metal characteristics, were investigated. Water and sediment samples were collected at four different points, each from four different terminals in Apapa Bay and, similarly, at Takwa Bay, which served as control due to its non-use for shipping. The surface water of the Apapa bay was characterized by the following ranges: 26.35–27.38ºC, 7.03–7.85, 1100–1588 µScm^− 3, and 77.28–72.85 ± 0.41 mg/L, for temperature, pH, conductivity, and total alkalinity respectively. The biochemical oxygen demand, BOD_5, and the chemical oxygen demand, COD, values 72.4–36.5 mg/L and 199.1–236.7 mg/L, respectively, were above the permissible limits. Low concentrations of phosphate, 0.363–0.652 mg/L, and sulphate, 36.92 ± 14.10–11.10 mg/L were recorded. Potentially toxic metals concentrations ranged: Cd (1.210–3.024 mg/kg); Fe (30.000–35.625 mg/kg); Pb (1.756–65.902 mg/kg); and Cu (10.859–13.423 mg/kg) and were compared with Takwa bay concentrations: 0.600 mg/kg; 6.876 mg/kg; 8.585 mg/kg and 10.859 mg/kg. Different Sediment Quality Guidelines (SQGs) were applied to assess the metal toxicity risk. Significant (p < 0.05) correlations were observed among Cd, Pb, Fe, and Cu suggesting similar sources for the metals. The SQGs classified Apapa Bay as heavily polluted in terms of Cd and Fe and non-polluted with Pb and Cu. These findings provide baseline data for future policies protecting Apapa Bay marine environments.

bay

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physicochemical

potentially toxic metals

pollution

The water resources of earth are the most threatened natural resources. Over the years, groundwater pollution has generated concern due to the increase in agricultural and anthropogenic activities such as the application of fertilizers, uncontrolled discharge of untreated sewage and industrial wastewater, and shipping activities. The annual percentage of groundwater for drinking and agricultural irrigation is estimated at 65% and 25%, respectively (Cantor et al. 2018). However, due to the decline in groundwater quality and quantity, the available 29% of the entire groundwater body area is incapable of meeting environmental and human needs (Cantor et al. 2018).

Therefore, environmental impacts and pollution control of the marine environment attracted more attention in port developments, operations, and management. International conventions now regulate shipping activities, and since Nigeria is a coastal country and a member of the international coastal communities, its case cannot be different. Africa, in general, and Nigeria, in particular, are facing serious water pollution, and it is one of the most difficult challenges for water professionals, including but not limited to environmental managers and hydrologists. In addition, urbanization and industrial activities have, in recent times, increased, therefore contributing negatively to the pollution of water bodies (Ewemoje and Samuel 2014).

One of the major contributors to water pollution is uncontrolled and untreated discharge of wastewater. Its negative effect results in increasing oxygen demands and nutrients, facilitating toxic algal growth, and destabilizing aquatic ecosystems (Nguyen et al. 2023). Moreover, as a result of fluctuating pH concentrations of water, the toxicity and solubility of potentially toxic metals such as Arsenic, As; Cadmium, Cd; Mercury, Hg; Copper, Cu; Manganese, Mn, and Iron, Fe (Sintorini et al., 2021) could be altered and thus, affecting the recreational use of water. Unregulated discharge of untreated wastewater loaded with nitrogenous compounds threatens the environment, causing an increase in the concentration of nitrogen and its compounds, such as ammonium nitrogen in water bodies, leading to eutrophication (Akinnawo 2023). Ward et al. (2018) reported that the potential health risks of nitrate in drinking water bodies above the threshold of 45 mg/L might result in a condition known as methemoglobinemia in infants.

Among the priority contaminants that significantly limit the advantageous use of water for different activities, such as home or industrial purposes, include but are not limited to potentially toxic metals. Their extended half-lives, non-biodegradability, and potential accumulation in internal organs make them highly hazardous (Uruchi and Pankaj 2011). The human body lacks an effective mechanism to eliminate them if present in the body, even at low concentrations. According to Hazrat et al. (2019), some potentially toxic metals, either in a free or absorbed form, have been reported to be carcinogenic. However, depending on the quantity and length of exposure, other pollutants in wastewater are hazardous (Hazrat et al. 2019) not only to humans but also to aquatic life (Zaynab et al. 2022) that would be carried along the food chain, leading to food contamination (Prabhat et al. 2019). The heavily polluted air, water, and soil caused by increased industrial and anthropogenic activities may be responsible for Nigeria's low life expectancy rate compared to many other countries.

Nigeria is one of the major oil-producing countries whose ports are used in loading, transporting, and unloading crude and refined oil cargo and the accidental discharges associated with tankers. Therefore, Nigerian ports are extremely vulnerable to contributing to the contamination of the country's maritime environment by discharging hazardous and toxic substances from the exploration and exploitation of oil and chemicals. Accordingly, port activities such as dredging, equipment upkeep and repairs, port infrastructure development, industrialization, cargo handling and storage, ship discharges (especially ballast waters), shore-based transportation, and accidents involving harmful material-carrying vessels that result in spills at ports can all contribute to environmental pollution in the port industry (Igbokwe 2001). The environmental threat posed by these activities has been totally neglected, mainly because all activities in Apapa Bay have been one of the government's sources of revenue. This may be part of the reasons little or no research has been conducted in this area when compared to some pollution potential studies such as Impact Assessment of Brewery Effluent on Water Quality in Majawe, Ibadan, South Western Nigeria (Alao et al. 2010), An Assessment of Environmental Safety of Shipping Operations at Apapa Port Lagos, Nigeria (Ojo 2020), Maritime Environmental Violations Within Nigeria and its Impacts (Maduekwe 2019), and Analysis of Marine Pollution of Ports and Jetties in Rivers State, Nigeria (Samson and Ofanson 2018). Preventing further pollution and exposure to sources of toxic pollutants is the mainstay of managing pollution. Therefore, this study focused on determining the degree of pollution at different bay terminals caused by shipping activities and, hence, identifying the terminal(s) with the most polluting activities.

2.1 Description of study area

This study was conducted in Apapa Bay situated in Apapa local government area, an industrial area of Lagos State, South West, Nigeria, as shown in Fig.1. Apapa Bay is a flat terrain, sand-filled, and concrete paved land area located on latitude 6^o27ꞌN and longitude 3^o21ꞌE. It lies within the tropical rainforest region with two distinct seasons: wet and dry. The annual temperature and rainfall range between 21^oC and 30^oC and 150 - 200 mm, respectively, with 88% humidity. The port operational area consists of berthing areas, cargo handling areas, stacking areas, and storage facilities (Abdul-Salam 2008).

2.2 Pretreatment of sampling bottles and storage containers

Before sampling, glass wares were soaked in 10 % HNO₃, and plastic containers were soaked in 1:1 HCl for 12 hours. Samples for dissolved oxygen (DO), biochemical oxygen demand (BOD₅), chemical oxygen demand (COD), and oil and grease determination were collected using glassware. In contrast, potentially toxic metals and samples of other physicochemical parameters were collected in plastic containers. Analar-grade chemical reagents and materials were used in the study.

2.3 Sample collection and preservation

Visitation was made to Apapa Bay to collect water and sediment samples, monitor, and conduct on-site analysis for physical parameters such as temperature, pH, and electrical conductivity (EC).

2.3.1 Water sampling

At various points in a regular interval of fifteen meters (15m) from the entry point to the berthing point, water samples were collected for characterization from four different terminals, namely: A.P Moller - Maersk Terminal, Apapa Bulk Terminal, Ship Repair, and Building Yard, and Petrochemical /Tank farm represented as Terminal A, B, C and D respectively within Apapa bay, Lagos, Nigeria as shown in Table 1. During sampling, the containers were rinsed with water to be sampled three times to avoid contamination. Each sample was collected in different containers with 1 mL conc. HNO₃ was added to it immediately to serve as a preservative and bring the pH < 2 for heavy metals analysis. Samples for DO were collected with DO bottles and preserved by the addition of Manganese (II) sulphate (MnSO_4(aq)) at the sites. In total, twenty water samples were collected and in accordance with the preservation method of Ademoroti (1996), all samples were taken to the laboratory and stored in the refrigerator at < 4^oC prior to analysis.

2.3.2 Sediment sampling

Sediment samples were collected by dredging from the sampling site into cellophane bags separately at every point where water was collected. The total number of samples collected was sixteen. The samples were then stored in a well-labeled cellophane bag.

2.4 Determination of the physicochemical parameters

In-situ determination of temperature, pH, and EC was carried out using a GMH Digital thermometer, Horiba LAQUA twin pH meter, and Oakton CON 6 conductivity meter, respectively, according to the method reported by the European Public Health Alliance, APHA (2005). The total solids (TS), total dissolved solids (DS), and total suspended solids (SS) were determined following the methods reported in the Guide Manual on Water and Wastewater Analysis, GMWWA (2000). In addition, DO, COD, BOD₅, chloride, and total hardness were determined using the titrimetric method, which was also reported by GMWWA (2000). However, the titrimetic method reported by APHA (2005) was used to determine total alkalinity. Sulphate (SO₄^2-) determination was carried out by turbidimetric method following the method of Tolulope et al. (2019), total phosphate by stannous chloride colorimetric method, while oil and grease was by partition – gravimetric method as reported by GMWWA (2000).

2.5 Chemistry of some methods for determination of physicochemical parameters

The chemical reactions during the determination of some of the physicochemical parameters were presented as supporting information.

2.6 Digestion of sediment sample

Akinbola (2012) reported method was used for drying, grinding, and sieving of the sediment samples, and the digestion procedure reported by Das and Ting (2017) was adopted. The filtrates were made up to mark with deionised water and agitated to mix well. Blank solutions were also prepared. The diluted filtrates were then analyzed for concentrations of potentially toxic metals.

2.7 Determination of total concentration of selected potentially toxic metals

The stock standard solutions (1000 ppm) of Cd, Pb, Fe, and Cu were purchased from Sigma – Aldrich, South Africa, from which sub-stock standards (100 ppm) for Cd, Pb, Fe, and Cu were prepared by dilution, after which working standard solutions of concentrations ranging 0.5 – 20 mg/L were prepared from the prepared 100 ppm by dilution. At different wavelengths, as presented in Table 2, measurements were done by Flame atomic absorption spectrometry (iCE^TM 3000 series, Thermo Scientific Instrument). Calibration curves method was then adopted. Nonetheless, prior to analyses, standards were run to check for the instrument’s performance and the detection limit. The quality assurance employed includes strict digestion procedures and procedural blank. Additionally, a spike recovery test was conducted on the sediment samples containing different concentrations of Cd, Cu, Pb, and Fe in order to validate the analytical methods that were employed. The recovery of the analyte was done by spiking accurately weighed 5.0 g of sediment samples from each terminal in Erlenmeyer’s flasks; two of which no standard was added, and to others, analyte standards of Cd, Cu, Pb, and Fe were added in an increasing volume pattern (2, 4, 6 and 8 mL) followed by digestion before being analyzed for potentially toxic metals with flame AAS. The recovery values expressed in percentages were calculated.

2.8 Statistical analysis

The correlation coefficient was evaluated using Statistical Program for the Social Sciences computer software package (SPSS inc., version 13), and significant differences between the concentrations of potentially toxic metal in each terminal and Takwa bay (control) were assessed using one-way analysis of variance (ANOVA) procedure.

Physicochemical parameters

The data from this research represent findings at the time of collection and may not necessarily reflect the seasonality to which the bay is truly exposed. The main characteristics frequently employed to assess the physicochemical properties of water are summarized in Table 3, amongst which pH, DO, COD, BOD₅, sulphate, phosphate, oil and grease, and most importantly, the potentially toxic metals were the main focus discussed.

The pH values of Apapa Bay's water were slightly alkaline, ranging from 7.03 ± 0.15 to 7.85 ± 0.21 (Table 3). These results aligned with the National Environmental Standards and Regulations Enforcement Agency, NESREA (2011) permissible limit of 6.5 – 8.5 for drinking and recreational purposes. Amongst notable characteristics of the marine environment is the stability of its pH, maintained by the biological activity of the coastal zone and is astonishingly constant over a specific area. Similar views of the pH results have been independently reported by Onyema et al. 2009; Balogun et al. 2011; Onyema 2013; on water samples within Lagos such as Badagry Creek, Lagos Habour and Iyagbe Lagoon.

Amongst the water quality control measures is the concentration of dissolved oxygen (DO). It is the amount of oxygen present in water, and its unit is mg/L. It is affected by the presence and destruction of organic substances and the self-purification capacity of the water body (Ma et al. 2020). As presented in Table 3, the dissolved oxygen concentrations from this study ranged from 2.59 ± 0.302 to 4.47 ± 1.316 mg/L. This is similar to those reported for many other polluted Nigerian waters, including the 3.90 to 4.95 mg/L of Apese lagoon (Victor and Onomivbori 1996), and the reported concentration range of 2.41 to 4.95 mg/L for some polluted water bodies in Nigeria (Edokpayi and Osimen 2001; Davies et al., 2009; Ogunfowokan et al. 2005). Some activities such as shipping, dredging, channeling, and anthropogenic and industrial activities release larger volumes of oxygen-demanding pollutants into the water system, thus contributing to low DO of the water. This leads to the extremely unpleasant nature of the water (Czarnota et al., 2023).

At 25^oC, the permissible limit of dissolved oxygen concentrations in unpolluted water ranges between 8 and 10 mg/L and concentrations ranging from 2 - 5 mg/L adversely affect aquatic life (Binod and Bhoj 2012). However, a concentration below 2 mg/L usually causes the death of aquatic animals (Small et al. 2014). Due to low dissolved oxygen present in water at high temperatures, the sustainability of aquatic organisms is affected. This study's DO values were below the suggested threshold. Major characteristics of polluted water is the low levels of DO cause by elevated BOD₅ and COD due to effluent waste materials discharged from ships and jetties into surface water. The value of BOD₅ is always lower than that of COD because many organic substances cannot oxidize biologically but can be oxidized chemically. Effluent waste, especially oil materials discharge from ships and jetties causes higher values of BOD₅ and COD. Generally, biological oxidation of organic pollutants is practically impossible. This accounts for higher COD values when compared with BOD₅. In this study, the principle was observed as COD concentration ranged from 199.1 ± 10.2 to 236.7 ± 14.8 mg/L while BOD₅ concentration ranged between 36.5 ± 4.6 and 72.4 ± 2.6 mg/L. The ratio of BOD₅ and COD varies widely from one terminal to another, an indication of differences in the types of organic compounds that might be present. The levels of BOD₅ and COD were not in agreement with the NESREA’s limit of 6.0 mg/L and 30.0 mg/L, respectively for wastewater. High level of COD is an indication of harmful conditions and the presence of non-biologically oxidizable matter, and high levels of BOD₅ indicates that there may not be enough oxygen present in the water of Apapa Bay for aquatic organisms such as crabs, crayfish, toad, and fish.

The concentrations of sulphate in this study ranged from 36.92 ± 14.10 to 64.28 ± 11.10 mg/L. However, according to NESREA (2011), the maximum contaminant level in wastewater is 500 mg/L. Therefore, the concentration of sulphate in Apapa Bay water is lower than the permissible limit. Most tropical waters have low nutrient values, a common feature of natural and polluted waters (Christian et al. 2021). The level of sulphaterecorded in this study is suggestive of organic pollution, which agrees with the work of Tolulope et al. (2019).

In Nigeria, NESREA’s maximum permissible limit for phosphate in polluted water is < 5 mg/L. Literature reports shows that studies of water bodies, for example, Lagos lagoon, showed low phosphate levels. Balogun et al. (2011) reported the phosphate levels of 0.57 – 1.60 mg/L for Lagos harbor, and Onyema et al. (2009) reported 0.28 – 2.50 mg/L for study of Badagry creek. The results of Chukwu and Akinyanmi (2018) were 2.05 – 4.34 mg/L for Apapa Waters, and Davies et al. (2009) reported 0.14 – 0.35 mg/L for Elechi Creek. However, the concentration of phosphate recorded in Apapa Bay water was at low range of 0.363 ± 0.116 mg/L to 0.652 ± 0.094 mg/L. Therefore, it is within the range of phosphate values reported in the above-mentioned studies. Phosphate is an essential part of nutrient needed by lants and animal for growth, hence its low concentration or absence would affect the growth of aquatic organism in Apapa Bay. Aside from the domestic and industrial effluents discharged into the bay, the level of phosphates (0.363 to 0.652 mg/L) recorded in this study could be attributed to the discharge of ballast water from ships and cargo sailing constantly on the water.

The presence of oil and grease in wastewater is a threat to wastewater treatment systems. In excess amounts, they may impede aerobic biological processes, leading to inefficiency and increased cost of wastewater treatment. When discharged in wastewater, they may cause surface films and shoreline deposits, causing environmental degradation (Wanda et al. 2021). In this study, the concentrations of oil and grease from Apapa Bay, presented in Table 3, are 13.03 ± 0.60 mg/L; 16.02 ± 1.17 mg/L; 16.33 ± 0.21 mg/L and 21.65 ± 0.28 mg/L for terminals A, B, C and D respectively. These values are above the regulatory authority, NESREA permissible limits of 0.1 mg/L.

Potentially toxic metals analysis

Examined from different sampling sites, the distribution of potentially toxic metals, namely Cd, Fe, Pb, and Cu, in the Apapa Bay bottom sediments has been analyzed to help understand the influence of shipping activities on the water quality of the Bay. The sampling sites are Terminals A, C and D, and Takwa Bay serves as control due to its non-shipping activities. The distribution patterns were represented by interpolating the metal concentration from the plotted calibration curve. Table 4 depicts the mean concentrations of potentially toxic metals analyzed. The results were then compared with some previously studied bays of the world, presented in Table 5. There is a wide range of values of the mean concentrations of the potentially toxic metals against those obtained from Takwa Bay (control) where the effect of shipping activities was low except copper which has the same values in almost all the Terminals; Cd (1.210 ± 0.001 to 3.024 ± 0.057 mg/kg); Fe (30.000 ± 0.884 to 35.625 ± 2.946 mg/kg); Pb (1.756 ± 0.170 to 65.902 ± 6.730 mg/kg); and Cu (10.859 ± 0.907 to 13.423 ± 0.907 mg/kg) while in Takwa bay (control), mean concentrations Cd (0.600 ± 0.001 mg/kg); Fe (6.876 ± 0.010 mg/kg); Pb (8.585 ± 0.510 mg/kg); Cu (10.859 ± 0.910 mg/kg).

Cadmium ranged from 1.210 ± 0.001 mg/kg (Terminal C) to 3.024 ± 0.057 mg/kg (Terminal A), and the control (Takwa bay) showed a low value of cadmium (0.600 ± 0.001 mg/kg). The cadmium level was lowest at Terminal C. These values are high compared with many other studies, such as 0.136 mg/kg (Wei et al. 2023); 0.4 mg/kg (Hakima et al. 2017); 0.11 mg/kg (Qiao et al. 2015), 0.12 mg/kg (Xu et al. 2015) and 0.35 mg/kg (Ebru 2012). Aside from the nearness of many industries to the study area that might increase the level of cadmium through their discharge of untreated wastewater, major remote sources with respect to shipping activities could be from ship construction, repair activities in the dockyard, and the use of motor vehicle tire rubber used by ships to maintain buoyancy. Cadmium is one of the major byproducts of zinc refining, a non-corrosive pigment used in the manufacturing of ship paint (Gunnar et al. 2015). It is extremely toxic (Janja et al. 2022), and studies have reported that consumption of aquatic organisms with high levels of cadmium leads to cardiovascular and skeletal malformation (Balali-Mood et al. 2021).

The Apapa Bay sediment concentrations for Pb ranged from 65.902 ± 6.730 mg/kg (Terminal C and D) to 1.756 ± 0.170 mg/kg (Terminal A), and the control (Takwa Bay) showed a low value of Pb (8.585 ± 0.510 mg/kg). The concentrations of Pb in the sediment samples of Terminal A and D are higher than the reported values of Weihai Bay, China (Wei et al. 2023); Upper Gulf, Thailand (Qiao et al. 2015); and Laizhou Bay, China (Xu et al. 2015). Meanwhile, Terminal B and Takwa Bay results are lower than the above-mentioned Bays. Petroleum products, certain geological formations, and anthropogenic sources in the nearby communities are the study area's main sources of lead (Pb). The most common form of Pb in the aquatic environment is Pb²⁺,and the dimethyl lead (CH₃)₂Pb²⁺ is a very good example (Chowdhury et al. 2022). Dimethyl lead (CH₃)₂Pb²⁺ is used to increase the octane rating of oil, making oil its major source of exposure. Therefore, the primary method of consuming this metal is through food, and consumption of aquatic organisms from the research region may raise the fatal dose in the human body. The toxicity of Pb has been adequately reported in some environmental studies, such as Hauptman et al. (2017), Wani et al. (2015), and Mandal et al. (2023).

The Apapa Bay sediment concentrations for Cu ranged from 10.859 ± 0.907 mg/kg (Terminal C, D, and Takwa Bay) to 13.423 ± 0.907 mg/kg (Terminal A). In this study, both Terminals C and D have the same mean concentration, while it is higher in Terminal A, probably as a result of the heavy use of copper mounts in shipbuilding. The level of Cu in all Terminals and that of Takwa Bay is lower than the reported values in literature such as Wei et al. (2023); Hakima et al. (2017); Qiao et al. (2015); Jamshidi and Saedi (2014); Xu et al. (2015); and Ebru (2012). However, the recently conducted study in Apapa jetty and Dadda water by Chukwu and Akinyanmi (2018) reported lower values, suggesting a high concentration of Cu. The high Cu concentration in this study could be attributed to sand mining and dredging activities. The values were, on average, four times lower than 47 mg/kg set by Swedish Environmental Sediments Quality Guideline, SESQG (1996), as presented in Table 4.

Higher values of Fe were found in all three terminals, with Terminal A in the highest concentration (35.625 ± 2.946 mg/kg). Terminal C had the lowest value (30.000 ± 0.884 mg/kg), while the control (Takwa bay) concentration was 6.876 ± 0.010 mg/kg. The low pH value of Terminal C may be accountable for the lowest content of iron in the sediment. This is because a decrease in pH value increases the solubility of many potentially toxic metals such as Al, Hg, Mn, and Fe (Sintorini et al. 2021). Iron is a trace element, nutritionally important, and aids metabolic processes. In this study, the iron concentrations were higher than the 4 mg/kg severe effect level by SESQG (1996), as presented in Table 4. This might be attributed to the dredging and landfilling operations by terrestrial sediments.

To safeguard aquatic biota from the detrimental and toxic impacts associated with sediment-bound pollutants, a number of Sediment Quality Guidelines (SQGs) have been developed to assess the degree of potential harm that the chemical state of sediment may cause to aquatic life and are intended to be used in the interpretation of sediment quality. They are also utilized in order to prioritize and rank contaminated areas for further research (Yanhao et al. 2018). Applying the Washington Department of Ecology Sediment Quality Guidelines (WDOE 1995), the Apapa bay is classed as non-polluted with respect to Pb. However, the elevated levels of Cd prompted the classification of the bay as a heavily polluted area. Portuguese legislation classification (attached as supplementary information) of sediment in the coastal zone classified the bay as clean dredge sediment in terms of Cu and trace contaminated sediment in terms of Fe.

Recovery studies

The summary of the results of the spike recovery tests is presented in Table 6, and it was evident from the percentage recoveries of the potentially toxic metals that the uncertainties of the analytical methodologies fell within acceptable limits, thus validating the accuracy of the calibration method employed.

Test of significance: Analysis of variance (ANOVA)

For the correlation analysis (Table 7), there was no significant difference between each terminal (A, C, and D) and that of Takwa Bay in terms of Cd and Cu. However, significant differences exist between all the terminals (A, C, and D) and Takwa Bay for Fe and Pb.

Correlation analysis of potentially toxic metals analyzed

The coefficient of correlation describes the degree of relationship between two continuous variables. Oftentimes, it is scaled in the range –1 through 0 to +1, where -1 indicates a perfect inverse relationship of the two comparing variables; 0 means that there is no linear association, and +1 describes a perfect linear relationship. An important oxide of Fe known as iron (oxyhydr) oxide is readily available in the environment, and due to its high surface areas and reactivity, it greatly influences the retention capacity of potentially toxic metal retention in surface sediment (von der-Heyden and Roychoudhury 2015). Literature reports that co-precipitation of potentially toxic metals in the presence of iron (oxyhydr) oxide is affected by total hardness (Ahn et al. 2018). More so, the solubility of metals, including potentially toxic metals such as Cu, Cd, Mn, and Fe, is inversely governed by the pH of the solution (Sintorini et al. 2021). Therefore, a correlation of the sediment’s iron contents, pH values and total hardness with the sediment's potentially toxic metals were analyzed. As illustrated in Table 7, most of the metals showed a close relationship with Fe. Thus, the results suggested that Fe is important and the cause of the metal enrichment in the sediments. Positive and significant correlation (p < 0.05) among Cd, Fe, Pb, and pH reveals the dependency of these metals on pH. The negative correlation observed for Cu with pH is suggestive of the metal not being associated with pH but can be attributed to other sources. In addition, the correlation matrix shows a significant and positive correlation among Cd, Cu, Fe, and Pb.

With the exception of sulphate, phosphate, DO concentrations, and temperature that were lower than the permissible limits, other physicochemical parameters monitored in all the Terminals (A, B, C, and D), including many of the corresponding potentially toxic metals concentrations monitored in Terminals A, C and D were not in compliance with the limit set by some World Water Quality Assessment and Monitoring bodies such as NESREA (2011). It was found that total solids, total dissolved solids, conductivity, total hardness, chloride, total alkalinity, oil and grease, BOD_5, and COD were higher than the set limits, while pH was slightly alkaline. This revealed the water degradation level due to uncontrolled shipping activities in one of the busiest bays in Nigeria, the port of Apapa, Lagos. Especially during the dry season, the accumulation of metal concentrations could be accelerated, presenting a severe risk to both the aquatic environment and those who feed on aquatic animals since it would be carried along the food chain. Considering the values recorded for the pollution indicators in this study, Apapa Bay surface water is contaminated with Terminal D (Petrochemical Tank/Farm), showing the highest contamination compared to the other Terminals. Although the level of pollution varies from one location to another, however, the bay appears to be generally polluted. The results revealed unfeasible conditions in Apapa Bay caused by an excess of shipping activities such as dredging, transportation, repairs and maintenance. It is hoped that this study will significantly encourage the Apapa Bay waste treatment authority to regularly assess, collate data, and properly document the environmental pollution conditions of Apapa Bay to the Nigerian Ports Authority (NPA). This is expected to create an avenue for adequate education of workers on the proper cleanup of all container port operations with the provision of a major channel for proper disposal of wastewater that must have been properly treated.

Author Contributions

All authors contributed to the study conception and design. Material preparation and data collection were performed by Taofeek Mayowa SALAMI and Matthew Adewale ADEGUNLE. The analysis was jointly performed by Taofeek Mayowa SALAMI and Adebayo Samson ADEYEMI. The first draft of the manuscript was written by Taofeek Mayowa SALAMI. The duo, Temilade Fola AKINHANMI and Hassan Omoniyi ADEBESIN made their corrections followed by proofreading of the final draft by Olukayode Olusegun ODUKOYA and Oladipo ADEMUYIWA. All authors read and approved the final manuscript.

Funding

This study was completely sponsored by the authors with no external support. Additionally, no support was received from any institution to cover cost of publishing.

Data availability: All data generated and analyzed during this work are included in this published article.

Ethics approval: Not applicable.

Consent to participate: All authors agreed to participate in this research project titled Environmental Impacts Assessment of Shipping Activities on Water Quality of Apapa Bay, Lagos, Nigeria.

Consent for publication: All the authors approved the manuscript for publication.

Declaration of competing interest

The authors declared that they have no known competing financial interests or personal relationship that could have appeared to influence the work reported in this paper.

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Table 1 Areas of private sector operation in Apapa bay, Lagos, Nigeria.

S/n	Company	Terminals/areas
A	A.P Moller-Maersk terminals	Apapa container terminal
B	Apapa bulk terminal	Apapa terminals A & B
C	Ship repair and building yard	Shipping department area
D	Petro-chemical /tank farm	Petrochemical department area

Source:Asabe 2021

Table 2 Wavelength of measurement for the potentially toxic metals

Element	Wavelength of main resonance line (nm)	Flame	Standard working range (ppm = mg/kg)
Cd	228.8	AA	0.5 – 2.0
Pb	217.0	AA	5.0 – 20.0
Fe	248.3	AA	1.0 – 4.0
Cu	324.8	AA	1.0 – 4.0

Key: AA = Air/acetylene

Table 3 Summary of physicochemical parameters of the studied terminals

Parameters /Sites

NESREA Limits

A

B

C

D

pH

Water temperature (^oC)

Conductivity (μS/cm)

Total dissolved solids (mg/L)

Total suspended solids (mg/L)

Dissolved oxygen (mg/L)

Biochemical oxygen demand (mg/L)

Chemical oxygen demand (mg/L)

Total alkalinity (mg/L)

Total hardness (mg/L)

Chloride (mg/L)

Sulphate (mg/L)

Phosphate (mg/L)

Oil and Grease (mg/L)

6.5-8.5

35

10-1000

500.0

0.75

5.0

6.0

30.0

3.0 – 50.0

500.0

350.0

500.0

3.5

0.1

7.25

27.38

1588

778.25

16.53

4.12

64.1

199.1

75.08

609.31

4965.5

36.92

0.472

13.03

7.15

27.13

1463

768.95 19.45

4.23

63.7

205.5

74.93

710.57

4567.8

20.82

0.363

16.02

7.03

26.35

1447

765.20

25.78

4.47

36.5

217.4

72.85

611.40

4573.6

64.28

0.652

16.33

7.85

27.12

1100

763.68

11.62

2.59

72.4

236.7

77.28

640.32

4445.4

59.49

0.607

21.65

A = A.P Moller - Maersk Terminal B = Apapa Bulk Terminal

C = Ship Repair and Building Yard D = Petrochemical /Tank farm

NESREA = National Environmental Standards and Regulations Enforcement Agency (2011)

Table 4 Mean concentrations oftoxic metals analyzed in sediment(mg/kg)

Toxic metal	SESQG	A	C	D	Takwa bay (control)
Cd	0.5	3.024 ± 0.057	1.210 ± 0.001	1.976 ± 0.056	0.600 ± 0.010
Fe	4.0	35.625 ± 2.946	30.000 ± 0.884	32.917 ± 0.880	6.876 ± 0.010
Pb	34.0	65.902 ± 6.730	1.756 ± 0.170	41.268 ± 6.380	8.585 ± 0.510
Cu	47.0	13.423 ± 0.907	10.859 ± 0.907	10.859 ± 0.910	10.859± 0.910

A = A.P Moller - Maersk Terminal C = Ship Repair and Building Yard D = Petrochemical /Tank farm

SESQG (1996) = Swedish Environmental Sediments Quality Guidelines

Table 5 Comparison of the experimental results with some previous bay studies of the world (mg/Kg)

Bay	Cd	Fe	Pb	Cu		References
Weihai Bay, China	0.136	NA	26.26	23.36		Wei et al. 2023
Dakhla Bay, Morocco	0.4	NA	71.3	17.30		Hakima et al. 2017
Upper Gulf, Thailand	0.11	NA	23.57	17.43		Qiao et al. 2015
Wetland Anzali, Iran	NA	45424	27.61	57.13	Jamshidi and Saedi 2014
Laizhou Bay, China	0.12	NA	21.9	22.0		Xu et al. 2015
Izmir Bay, Turkey	0.35	3.41	128.92	45.98		Ebru 2012
Apapa Bay, Nigeria	0.60 – 3.02	6.88 – 35.63	1.76 – 65.90	10.86 – 13.42		Present study

NA = Not detected.

Table 6 Recovery studies

S/N	Metal	Average percentage recovery (%)
1	Cd	97.7 ± 3.53
2	Pb	91.6 ± 2.02
3	Fe	86.6 ± 4.83
4	Cu	91.2 ± 9.96

N = 4

Table 7 Correlation analysis

Variable	Cd	Fe	Pb	Cu	pH	Total hardness	Temp.
Cd	1
Fe	1.000	1
Pb	.975	.980	1
Cu	.907	.898	.792	1
Pb	.172	.192	.385	-.551	1
Total hardness	-.149	-.129	.073	-.551	.948	1
Temp.	-.871	-.829	-.924	-.499	1.000	-.448	1

Correlation is significant atp < 0.05

N = 6

No competing interests reported.

SUPPORTINGINFORMATION.docx

Environmental Impacts Assessment of Shipping Activities on Water Quality of Apapa Bay, Lagos, Nigeria

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Abstract

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1.0 INTRODUCTION

2.0 MATERIALS AND METHODS

3.0 RESULTS AND DISCUSSION

4. 0 CONCLUSION

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References

Tables

Additional Declarations

Supplementary Files

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