Dataset for PCBs and OCPs in intertidal sediment and surface-mixed layer water from Lagos lagoon, southwest coast of Nigeria

Sediment quality and the integrity of coastal aquatic ecosystems are deteriorating, particularly in regions with unregulated discharges of chemical pollutants into the environment. Although organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) have been banned in recent decades for their adverse effects on the environment and human and animal health, these organic micropollutants are frequently detected in many aquatic systems. This dataset reports baseline concentrations of 27 PCBs and 20 OCPs analysed in surface-mixed layer water and sediment samples collected from designated sampling locations in the Lagos lagoon, off the Gulf of Guinea, Nigeria. The EPA Method 3570 (SW-846) and EPA Method 3510C (SW-846) with slight modifications were used for sediment and water extraction/cleanup procedures, respectively. Data were acquired using gas chromatography (GC) Agillent 6890 and 5890 equipped with electron capture detector (ECD). Data are reported in ng/L and µg/kg for concentrations of OCPs and PCBs in surface-mixed layer water and sediment samples, respectively. The interpretation of this dataset is fully discussed in the related research articles by Benson et al. (2023) and Unyimadu and Benson (2023).

Although organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) have been banned in recent decades for their adverse effects on the environment and human and animal health, these organic micropollutants are frequently detected in many aquatic systems.This dataset reports baseline concentrations of 27 PCBs and 20 OCPs analysed in surface-mixed layer water and sediment samples collected from designated sampling locations in the Lagos lagoon, off the Gulf of Guinea, Nigeria.The EPA Method 3570 (SW-846) and EPA Method 3510C (SW-846) with slight modifications were used for sediment and water extraction/cleanup procedures, respectively.Data were acquired using gas chromatography (GC) Agillent 6890 and 5890 equipped with electron capture detector (ECD).Data are reported in ng/L and μg/kg for concentrations of OCPs and PCBs in surface-mixed layer water and sediment samples, respectively.The interpretation of this dataset is fully discussed in the related research articles by Benson et al. (2023) and Unyimadu and Benson (2023) Data were acquired using gas chromatography (GC) combined with electron capture detection (ECD)Instruments: • Agilent GC-ECD Model 6890 with 63 Ni ECD equipped with a Rtx 5 fused capillary column (30 m x 0.25 mm inner diameter x 0.5 μm).• A Hewlett Packard Model 5890 Gas Chromatograph Series 11 coupled with an electron capture detector.The temperature conditions of the oven column were as follows: initial 180 °C (for 1 min), increased by 10 °C/min to 225 °C and ramped to 250 °C at 10 °C/min (held for 10 min).The temperature of injector and detector was maintained at 250 °C and 325 °C, respectively.Purified N 2 gas (99.99%) served as the carrier gas and was maintained at a flow rate of 1.0 mL/min.

Value of the Data
• Comprehensive baseline data on polychlorinated biphenyls (PCBs) and organochlorinated pesticides (OCPs) in the intertidal sediments and surface-mixed layer water of Lagos lagoon is presented.• Sampling, analytical methods, and data described in this article will be helpful to researchers interested in organic micropollutants in aquatic environments, particularly individuals conducting systematic and meta-analysis reviews.• Using these data, researchers can determine the primary sources of OCPs and PCBs, their environmental fate and toxicity.• These data can be used in future environmental monitoring studies to determine the ecological and health risks posed by OCP and PCB exposures.• The data could assist policymakers in selecting site-specific monitoring and remediation strategies to address contamination concerns.

Objective
The primary objective of this dataset is to provide baseline information on the pollution status of an important microtidal lagoon system using sediment and water samples obtained during a multi-location sampling survey.We investigated and determined the concentration and spatial distribution of PCBs and OCPs in sediment and surface-mixed layer water samples from Lagos lagoon, Nigeria [1][2][3] .Additionally, we estimated the potential ecological risk using sediment quality standards as well as the health risks associated with organism-level exposure to target organic micropollutants.

Surface-mixed layer water sampling
Water samples were collected during the sampling period using a Van Don water sampler.The Van Don sampler used was manually operated and have open tubes of known volume fitted with a closure mechanism at each end.The water sampler was constructed of stainless steel.The sampling device is lowered on a calibrated line to the specific sampling depth, the sample is taken and the top and bottom lids are closed.500 mL amber glass bottles that were used for the collection of surface and bottom water samples were completely decontaminated by washing in detergent to remove any solid residues, soaked for 24 h in an acid bath (chromic acid wash; 100 mL of concentrated H 2 SO 4 slowly and with constant stirring to a solution of 5 g of sodium dichromate in 5 mL of water).The bottles were rinsed with deionized distilled water twice and allowed to dry in an oven over night.The bottles were rinsed twice with hexane.

Intertidal sediment sampling
A total of 54 sediment samples were collected from the sampling locations.Motorised boat was used for grabbing at all the locations.The upper 15 cm of the surface sediments were sampled from the sampling sites with a Birge-Ekman sediment grabber in areas of low flow velocity ( < 0.30 m/s).Immediately the grab is lifted to the boat a stainless-steel scoop precleaned with acetone was used to collect about 100 g of the sediment sample into a precleaned 200 mL amber glass bottled.The sample was preserved in a cooler with ice blocks.Immediately on land the sampled were preserved in a deep freezer to avoid degradation.Samples were stored for the shortest possible time interval between sampling and extraction/cleanup.

Sediment extraction
The procedures EPA 3570 with slight modification were used [8] .Approximately 5.0 grams of anhydrous sodium sulfate was added to a precleaned mortar and 5 grams of fresh wet sediment was added to the mortar and homogenized to a complete mixture.The mixture was carefully transferred to a pre-cleaned PTFE extraction tube which has a PTFE screw cap. 5 to 10 precleaned glass beads were added.25 mL of a mixture of acetone and petroleum spirit (1:1) was added to the PTFE extraction tube; the extraction tube was tightly capped and allowed to stand for minimum of 20 minutes.This allows complete permeation of solvent to the matrix.20 μg/L of the internal standard decaflourobiphenyl in iso-octane directly added to the sediment and sodium sulphate mixture.The tube was shaken vigorously until the slurry is free-flowing.Any chunks were broken with the metal spatula, working quickly but gently.The cap was replaced immediately after the breaking of the chunks.More sodium sulfate was added and manually mixed as necessary to produce free-flowing, finely divided slurry.The samples were extracted by rotating end-over-end for at least 30 minutes.Care was be taken to release pressure by opening and closing the flasks at intervals.
The solids were allowed to settle to settle for one to two minutes.The solvent layer was filtered through a small glass funnel containing a layer of anhydrous sodium sulfate over a plug of glass wool into a receiving conical flask.The sodium sulfate was thoroughly pre-wetted with acetone.The sodium sulfate was rinsed with 2 to 3 mL of acetone as Soon as the surface is exposed.The top of the sodium sulfate layer was not allowed to go dry.The sediment sample was extracted twice more by adding approximately 15 mL of acetone/petroleum spirit mixture to the sample, capping the extraction tube tightly, and shaking vigorously by hand for 2 minutes.All the extracts are combined and poured into the round bottom flask of the rotary evaporator.The round bottom flask of the rotary evaporator is placed in a constant temperature hot water bath so that the concentrator flask is partially, but not completely, immersed.The temperature of the bath was adjusted and the position of the apparatus so that the solvent heat evenly.The sample volume was reduced to approximately 1.0 mL.

Extraction procedure for water
The method employed is EPA method 3510C with slight modifications [9] .25 mL of dichloromethane was added to 250 mL of water sample (unfiltered) in its original sample bottle.The bottle was closed tightly with an aluminium lined cap.20 μg/L of internal standard, decafluorobiphenyl was added.The bottle was shaken manually for 15 minutes so that the vortex formed at the surface reaches almost to the bottom of the bottle.The contents of the bottle were transferred to 500 mL separatory funnel.10 minutes was allowed for the aqueous and the organic phase to separate.The organic layer was transferred to 250 mL separatory funnel and the aqueous layer was returned to the sample bottle.The 500 mL separatory funnel was rinsed twice with dichloromethane; 10 mL at first and then 15 mL, transferring the solvent to the sample bottle after each rinsing.
The shaking, separation and rinsing procedures were repeated twice.After the third separation the organic layer was transferred to the 250 separatory funnel and the sample discarded.The 500 mL separatory funnel was rinsed again and the contents added to the 250 mL separatory funnel.The 250 mL separatory funnel was shaken for 2 minutes and allowed to stand for 10 minutes.5 cm 3 of anhydrous sodium sulfate was placed in a 125 mL sintered glass funnel, was set up to drain into a 250 mL round bottom flask.The organic layer in the 250 mL separatory funnel was drained into the filtration column.15 mL of dichloromethane was added to the aqueous layer remaining in the separatory funnel and shaken for 2 minutes and then allowed to stand for 10 minutes.The organic layer was drained again through the sodium sulfate filter column and the remaining aqueous layer phase discarded.The 250 separatory funnel was rinsed twice with 10 mL of dichloromethane and passed through the sodium sulfate column.The sodium sulfate column was washed with 10 mL of dichloromethane.The column was removed and 1.5 mL of iso-octane was added to the 250 mL round bottom flask as a keeper.The combined sample extracts were evaporated under vacuum using a rotary evaporator at 30-35 °C to 5 or 6 mL.The concentrate was transferred with 4 ×1 mL rinsings to a 15 mL graduated glass tube with conical bottom.The evaporation was finished to 3 mL under gentle stream of nitrogen at 50 to 60 °C (water bath) at atmospheric pressure.The extract is solvent exchanged to iso-octane.

Cleanup for water and sediment
A 600 mm x 19 mm i.d.cleanup column was prepared by blocking the hole with glass wool and adding 3g of activated silica gel (60 to 100 mesh, calcined at 650 °C for 24 h, and then stored at 130 °C until use.The column was topped with 1 cm of preheated Na 2 SO 4 previously heated at 650 °C for 18 h, and stored in a clean bottle in a dessicator.The column was eluted with 40 mL hexane and discarded.The concentrated extract in iso-octane was transferred to the column and eluted with 50 mL of 20 + 80 DCM/hexane (v/v ratio).The eluent was collected in a 100 mL round bottom flask.This fraction (referred as eluent 1) contains PCBs and about 14 °C.
The elusion was continued with another 50 mL of 50 + 49.65 + 0.35 DCM/hexane/acetonitrile mixture and the eluate collected in another 100 mL round bottom flask.This fraction called eluate 2 contains endosulfan, dieldrin, endrin, and methoxychlor.The eluates are reduced by volume with rotary evaporator to 3 mL and solvent exchanged to iso-octane and the volume is further reduced to 1 mL in a stream of nitrogen.

Limitations
Lack of historical data on PCBs and OCPs levels in intertidal sediment and surface-mixed layer water in the lagoon ecosystem made it challenging to evaluate long-term trends and impacts.Besides, limited budget constrained the scope of target micropollutants' analysis, the length of seasonal campaign, and the number of sampling locations considered in this study.
Sediment quality and the integrity of coastal aquatic ecosystems are deteriorating, particularly in regions with unregulated discharges of chemical pollutants into the environment.
. © 2023 The Authors.Published by Elsevier Inc.This is an open access article under the CC BY license ( http://creativecommons.org/licenses/by/4.0/ )

Table 1
Locations of sample collection and descriptions of potential contamination sources.

Table 5
Concentration (μg/kg) of endrin and metabolites in sediment samples.

Table 6
Concentration (μg/kg) of DDT and metabolites in sediment samples.

Table 7
Concentration (μg/kg) of endosulfan and metabolites in sediment samples.

Table 9
Concentration (ng/L) of PCBs in water samples from the Lagos lagoon.

Table 10
Distribution and concentrations of polychlorinated biphenyl species groups (di-PCB -nona-PCB) at each sampling location.