Warrington Environmental Pollution and Soil Health Risks

Report on the environmental pollution and human health risks of soils in the former industrial area of Woolston, Warrington.

2.Introduction:

As a result of rapid population growth followed by intense industrial activity and petrochemical development soils have suffered from contamination with substances of various origins (E.M.Garcia et al,2015).As a result of rapid industrialisation of cities such as Manchester, newly constructed canals were built all over the UK in order to increase trade as well as the exportation of goods. In the 1820’s, a new canal was established along the river Mersey with the purpose of shortening the route of navigation through the meandering Mersey.

3.Study site.

According to Warrington borough council, the New Cut Canal was opened in 1821. This 2km long canal was built in order to improve the Mersey and Irwell navigation by creating a shortcut for barges carrying goods between Liverpool and Manchester. Historical ordnance survey maps from 1907 show an adjacent chemical works, a large tannery, a slaughter house, a metal works and a gunpowder mill. Sustained industrial activity meant that the canal sediment was undoubtedly polluted by spillages from ships and industrial effluents (Hartley and Dickinson,2010). Following the establishment of the Manchester shipping canal the New Cut Canal began to decline until it was left derelict (Warrington borough council) and eventually the Canal was disconnected from the river and abandoned in 1978 (Hartley and Dickinson,2010). In that year, it was decided that the site was to be used for tipping under emergency procedures to deposit road construction rubble (Hartley and Dickinson ,2010).

Following this history, it has been estimated that the site contains 9800 tonnes of polluted anoxic sediment. It is known that this polluted sediment contains elevated levels of TPH’s (Total Petroleum Hydrocarbons), PAH’s (Polycyclic Aromatic Hydrocarbons) followed by highly elevated concentrations of metals (Pb, Zn, Cu, Cr and Ni) and Arsenic (As) (Hartley and Dickinson,2010).

4.Methods:

4.1. Methods out in the field.

4.1.1 Soil samples

To determine the degree of soil contamination at the site, soil samples were taken at various points along the New Cut Canal site. It was decided that a systematic sampling method would be used in order to record an adequate amount of data for the investigation. This sampling method had been chosen as it allowed one to determine the spatial pattern of contamination whilst limiting human errors (O1). Whilst at the site, transects had been established along the New Cut Canal site. Transects were established along a 700-metre stretch of the canal and each transect had been separated by 70 meters. In total there was 10 transects and along each transect,6 soil samples were taken approximately every 10 meters from the Northernmost point of the canal to the southernmost point closest to the river Mersey.

Soil samples from each sampling point were taken just below the surface but in order to prevent large organic materials from interfering with the soil investigations later it was decided that each sample should be taken and the large organic matter (Roots etc.) should be removed. This was done using a measuring tape and a spade. The soil samples had been gathered in plastic bags.

4.2. Conductivity and resistivity values within the soil surrounding New Cut Canal.

4.2.1. Electrical Resistivity Imaging (ERI) using ERT (Electrical Resistivity Tomography)

The ERI was used to show the potential mobility of trace and toxic metals within the soil by analysing conductivity data from the ERT and the EM-31. Conductivity measurements were taken using an ERT along a single transect measuring 35 metres between the New Cut Canal site and the river Mersey. The ERT takes conductivity measurements through a series of electrodes which are placed into the ground. Once these electrodes had been implanted and connected to each other via multi core cables a current was then injected into the ground through these electrodes and as the current passed through the soil resistivity measurements were taken. Changes in conductivity reflect variations in subsurface materials and higher conductivity readings are associated with higher metal concentrations in soil pore waters.

Figure 1: Below is an image that shows the standard setup of ERT. In this investigation the electrodes were inserted into the ground at distances of 2 meters apart. The transect of electrodes covered an area between the New Cut Canal and the river Mersey and was carried out at an angle of 0^° (North to South). Image from Terra Dat:  http://terradat.co.uk/survey-methods/resistivity-tomography/

4.2.2. Geonics EM-31 Ground Conductivity meter

ERT maps out the geological variations associated with changes in conductivity (Exploration instruments) as well as the EM-31. Unlike the ERT, the EM-31 gathers its readings by creating an electromagnetic field in the air using a coil wire which is separated from a receiver coil by 3.66 meters. The transmitted energy propagates into the subsurface where a second electromagnetic field is created due to the effect of soil moisture, conductive earth materials and other buried objects (Reynolds international,2011). The EM-31 is useful to this investigation as it can take conductivity measurements below 2 meters of the Earth’s surface. The data collected by both the EM-31 and the ERT could then be combined to determine changes in conductivity up to a depth of 3-4 meters.

4.3. Soil sample experiments in the lab

4.3.1. Determining total metal concentrations

Following the onsite extraction of soils samples, they were then taken to the lab for further processing. Before any more investigations were conducted the soil samples were dried in an oven at 40°C for 48 hours in order to remove all of the moisture.  Oven drying the sediment is crucial in this type of investigation as one can only compare the dry weight to the Soil Guideline Values (SGV’s) (DEFRA, 2002). Once they had been dried, the soil samples were then processed further in order to analyse the total metal concentrations (Pb,Zn,Cr and As), bioavailability of those metals, organic matter content and soil pH. Soil samples were then sieved so that larger particles greater than 2mm in diameter were removed.  After the samples had been sieved, analysis of the bioavailability of metals was conducted. 10g of sieved sediment was then added to a conical where 50mL of 0.5mol acetic acid was added using a measuring cylinder. Once the acid was added the flask was sealed with Parafilm and placed onto an orbital shaker for 30 minutes. Whilst the samples were shaken, 2 30mL universal sample tubes were prepped (2 for every sample) and a Whatman no 1 filter paper was added to each of the tubes. After the cylinder samples had been shaken, they were left to stand for 10 minutes in order for the contents to settle (Beneficial to the investigation as it sped up the filtering process). Following 10 minutes, the supernatant liquid in the cylinder was then added into the universal sample tubes through the filter paper. Once one of the tubes was full the second one was then introduced to the filtering process. Eventually both universal tubes were sealed and then analysis of the metal concentrations was conducted by Atomic Absorption Spectroscopy (AAS).

4.3.2. Determining organic matter (OM) content

Secondly, organic matter content needed to be measured, this was done using the loss on ignition method. This process began with the weighing of an empty porcelain crucible (W1). Soil was then added until it filled the crucible and was then weighed (W2). The air-dry weight was then determined by using the following calculation W2-W1. The minute that this was done the crucibles for each of the samples was then oven-dried at a temperature of 105°C overnight and then placed in a desiccator the following morning. Afterwards, the samples were then measured again (W3). The crucibles were then placed into a muffle furnace and ignited at 450°C for 8 hours and left to cool on a sand tray. After this, the crucibles were weighed again (W4). This was done to burn off any of the Organic Matter (OM) content. Muffled weight was then determined by using this calculation, W4-W1. The final method involved a simple calculation, shown below:

OM content (% of dry sediment) =

[oven dry weight (g) – muffled weight (g) / oven dry weight (g)] x 100

4.3.3. Determining soil pH

To begin with 10g of soil was added to a beaker using a spatula where it would then be mixed with 25mL of deionised water using a measuring cylinder. The beaker was then stirred well until all of the material had been suspended (To allow the contents to mix) shortly followed by a 15-minute period whereby the beaker was left to stand. Following the 15-minute period a pH strip was dipped into each of the samples. Using a pH reference card, the colours recorded on each of the pH papers was noted.

4.3.4. Determining Total (T) metal concentrations using XRF (X-Ray Fluorescence Spectroscopy)

Finally, 10g of each sample was added into a small plastic bag and then shaken until all of the soil reached the bottom. The bag was then placed onto the test bed and then the XRF machine determined the % values of Pb, Zn, Cr and As.

5. Results

5.1.

Figure 2: The table below shows all of the data collected from the field as well as metal concentrations in mg/kg^-1 for each of the soils samples. OM or organic matter was measured in grams. Total Chromium concentrations when analysed however the concentrations were too low when measured using X-Ray Fluorescence Spectroscopy (XRF).

SiteID	x	y	OM	pH	PbT	ZnT	CrT	PbB	ZnB	CrB
A1	363081	389035	4.66	5.50	29.00	199.00	nd	0.01	12.71	0.21
A2	363081	388969	14.81	5.80	15.00	80.00	nd	0.09	1.90	0.20
A3	363087	388919	15.28	6.00	20.00	130.00	nd	0.01	11.95	0.26
A4	363064	388867	6.26	4.70	645.00	417.00	nd	2.44	35.99	0.45
A5	363070	388823	10.67	4.50	40.00	205.00	nd	0.18	5.87	0.17
A6	363079	388737	8.76	4.50	58.00	299.00	nd	1.05	19.16	0.04
B1	363137	389021	23.24	5.00	178.00	32.00	nd	0.41	26.42	0.18
B2	363139	388973	6.83	5.00	79.00	16.00	nd	0.01	0.01	0.18
B3	363140	388941	7.02	5.00	126.00	24.00	nd	0.01	5.37	0.16
B4	363145	388882	13.11	4.70	128.00	27.00	nd	0.01	9.92	0.11
B5	363160	388808	10.16	4.70	96.00	26.00	nd	0.30	10.23	0.15
B6	363186	388731	13.57	4.70	184.00	32.00	nd	0.00	9.57	0.18
C1	363196	388941	9.10	4.70	73.00	21.00	nd	1.55	8.20	0.22
C2	363194	388975	10.60	5.00	107.00	19.00	nd	0.01	11.02	0.31
C3	363185	389022	11.20	5.00	79.00	24.00	nd	0.15	10.72	0.24
C4	363205	388828	13.10	4.70	75.00	20.00	nd	0.01	9.09	0.12
C5	363201	388854	8.90	4.70	93.00	20.00	nd	0.26	11.13	0.12
C6	363187	388888	9.60	4.40	95.00	24.00	nd	0.01	8.71	0.16
D1	363251	388969	7.51	6.10	126.00	298.00	nd	0.69	61.88	0.41
D2	363250	388965	10.55	5.80	111.00	278.00	nd	0.01	17.75	0.20
D3	363256	388999	11.45	5.50	109.00	312.00	nd	0.16	18.38	0.16
D4	363247	388907	12.92	6.10	32.00	45.00	nd	4.75	36.60	0.37
D5	363250	388898	9.32	5.00	34.00	56.00	nd	4.50	25.35	0.30
D6	363252	388887	3.86	4.40	23.00	32.00	nd	4.59	27.91	0.34
E1	363398	388984	7.70	5.50	38.00	298.00	nd	0.52	21.28	0.17
E2	363389	388997	8.90	5.90	55.00	433.00	nd	0.21	25.96	0.22
E3	363380	389003	5.60	5.10	38.00	532.00	nd	0.01	3.60	0.15
E4	363445	388929	11.20	4.50	21.00	56.00	nd	0.11	0.01	0.09
E5	363444	388919	11.90	5.10	19.00	48.00	nd	0.58	0.42	0.09
E6	363447	388907	12.10	5.20	33.00	63.00	nd	1.22	5.42	0.14
F1	363519	388982	9.77	5.80	33.00	225.00	nd	2.01	11.29	0.63
F2	363510	389010	11.16	5.50	22.00	134.00	nd	0.37	16.08	0.35
F3	363512	389029	5.70	6.50	55.00	489.00	nd	0.07	23.22	0.17
F4	363519	388973	6.89	5.00	37.00	220.00	nd	1.75	16.22	0.58
F5	363525	388946	6.18	4.70	21.00	80.00	nd	0.01	0.01	0.14
F6	363533	388923	6.75	4.40	20.00	52.00	nd	0.01	2.59	0.12
G1	363573	389056	21.17	5.80	43.00	287.00	nd	0.00	13.66	0.41
G2	363564	389032	12.76	5.50	45.00	289.00	nd	0.01	10.49	0.44
G3	363561	389022	8.53	7.00	32.00	212.00	nd	0.09	9.90	0.34
G4	363564	389001	8.32	5.00	23.00	176.00	nd	0.07	2.10	0.15
G5	363559	389022	6.67	4.70	21.00	76.00	nd	0.05	2.30	0.17
G6	363569	388965	8.35	4.70	19.00	34.00	nd	0.03	2.10	0.18
H1	363685	389056	6.26	6.50	1047.00	1639.00	nd	16.57	49.79	0.67
H2	363674	389036	2.22	5.50	49.00	1156.00	nd	0.17	38.15	0.22
H3	363669	389016	3.01	5.30	46.00	153.00	nd	8.73	23.47	0.44
H4	363632	388981	4.96	5.00	23.00	77.00	nd	0.24	2.97	0.06
H5	363631	388971	7.34	5.00	31.00	143.00	nd	0.46	6.01	0.11
H6	363632	388959	4.84	5.00	48.00	78.00	nd	2.44	0.64	0.13
I1	363697	389018	21.17	5.80	32.00	819.00	nd	0.74	40.06	0.39
I2	363703	389044	12.76	5.50	51.00	483.00	nd	1.65	32.53	0.60
I3	363694	389078	8.53	7.00	32.00	202.00	nd	2.10	25.27	0.81
I4	363718	388982	8.32	5.00	23.00	91.00	nd	0.48	9.23	0.12
I5	363720	388981	6.67	4.70	19.00	68.00	nd	0.01	0.01	0.05
I6	363723	388978	8.35	4.70	31.00	126.00	nd	0.01	7.46	0.09
J1	363775	389003	6.26	6.50	33.00	224.00	nd	2.22	26.49	0.80
J2	363770	389053	2.22	5.50	24.00	104.00	nd	0.01	0.37	0.13
J3	363767	389104	3.01	5.30	36.00	401.00	nd	0.40	25.69	0.33
J4	363771	388972	4.96	5.00	24.00	176.00	nd	0.01	10.96	0.18
J5	363771	388973	7.34	5.00	23.00	128.00	nd	0.01	11.93	0.19
J6	363772	388970	4.84	5.00	17.00	79.00	nd	0.01	4.30	0.09

 

Figure 3: The image below shows the spatial pattern of Lead (Pb) contamination across the New Cut Canal site. The image was created using Arc Map software. It is clear that the highest levels of Pb were found around sample site A3-5 and H1-2.

Figure 4: The image below shows the spatial pattern of Zinc (Zn) contamination across the New Cut Canal site. The image was created using Arc Map software. Based on the spatial image, it is clear that the highest levels of Zn were found around sampling sites H1 and H2.

Figure 5: The image below shows the spatial pattern of pH levels across the New Cut Canal site. The image was created using Arc Map. The most acidic pH readings were located towards the Southwest of the site whereas pH readings in the Eastern part of the sampling site increased to a pH of 5.3 and above.

Figure 6: The graph below represents the changes in the Total (T) metal concentrations of various metals as well as indicating how bio available these metals are in the area.

Figure 7: The stacked column below allows one to determine the bioavailability of Zinc as a percentage when compared to its total (T) metal concentrations for each of the sample sites. Upon observing the data, it is clear that (in terms of percentage) Zn bioavailability is greater towards the West end of the study site.

Figure 8: The stacked column below allows one to see the bioavailability of Lead (Pb) as a percentage when compared to its total (T) metal concentrations for each of the sampling sites. Based on a simple observation, it is clear that the bioavailability of this metal remains considerably low when compared to its total (T) concentrations. The highest bioavailability percentages are found within sample sites D6 and H3.

Figure 9: The image below is a general 25cm-resolution lidar image, assembled in GIS and with the position of the ERT line superimposed.

6.Discussion:

6.1. Spatial patterns of different contaminants at the site (O1)

In regards to the UK’s Soil Guideline Values, the concentrations of Pb found across the site at Woolston do not exceed (Most samples) the SGV for this metal which is set at 750 mg/kg in industrial soils (Environmental Protection Agency, 2009). One sample located towards the North-East part of the study site known as H1 contained a Pb concentration of 1047 mg/kg which is cause for concern however because it was the only sample which recorded this level it could be said that this could be an anomaly or alternatively that the metal concentrations located here have not become mobilised (Justifying why only one sample recorded such a high level). However, in another investigation Pb levels were noted to be higher in deeper layers of the canal sediment, further illustrating their mobility under anoxic conditions (Hartley and Dickinson,2010). This limits the strength of our conclusion as soil samples were only extracted at shallow depths (Around 5-10cm below the surface) and so the exact concentrations and mobility of Pb below the surface are unknown.

According to the EPA (2009), Zn SGV’s have not been established however Dutch Intervention Values were set at 720 mg/kg.  Both samples H1 and H2 exceeded the Dutch Intervention Values with 1639 mg/kg (H1) and 1156 mg/kg (H2) meaning the soils were quite contaminated with this metal. Despite this, alongside Pb levels, the majority of soil sample concentrations for Zn show concentrations far below the DIV’s.

Both As (Arsenic) and Chromium (Cr) had their metal concentrations analysed using the XRF machine however the readings were far too low and were removed from further investigations as they were found to be around the normal level of concentrations. However, in a previous study soil As concentrations varied between 20 and 90 mg/kg with a mean of 87.40 mg/kg (Hartley and Davidson, 2010). According to the EPA (2009), As SGV’s stand at 500 mg/kg (Industrial) and 20 mg/kg (Residential) therefore As concentrations can pose a risk to the local residential centres especially if the metal becomes mobile and contaminates ground water systems and the river Mersey. Cr levels were analysed by the XRF machine however the concentrations were so low that all of the sample site concentrations were left as ‘not defined’ (df) (Figure 2).

Spatial variations for pH show relatively similar readings across the sampling site and range between 4.8 and 5.8. This indicated that the soil

6.2. Determine the potential environmental mobility of trace and toxic metals

With regards to bioavailable form in Zinc, the highest levels recorded were located towards the North West of the sampling site with samples B1, D5 and E1 which recorded bioavailability (When analysed in Total concentration) percentages around the 40% or higher. However, the bioavailability of Pb was much lower in all samples where the largest percentages were recorded at around 15-20% of the total metal concentration.

In order to determine whether there was a relation between OM/ pH and metal concentrations a Spearman’s Rank Correlation test was applied. With regards to OM and pH the r_s (correlation coefficient) was -0.108 which meant that there was a very weak (-ve)correlation. On the other hand, the relationship between pH and ZnT were measured and came back with an r_s value of 0.5803 which was statistically significant meaning ZnT influenced pH readings. The higher the ZnT the higher the pH  along the sampling site.  Another test was used to determine the relationship (if any) between pH and PbT. The results came back with an r_s value of 0.02669, this is a very weak correlation and so it can be said Pb had little to no effect on the pH in the soil.

Despite most metals in the soil samples stating at relatively low concentrations it is important to note that the heavy metal concentrations observed in the North East area (Highest recorded levels) are cause for concern. They are a cause for concern as Green Waste Compost (GWC) has been applied to the site as surface mulch to improve the existing habitats but in doing so, this has had a negative impact on metal mobility. GWC contains large amounts of Dissolved Organic Carbon (DOC) which can assist in the transfer of metal(loids) through the soil as organic complexes because DOC is the most mobile fraction of organic ligands that exist in soils (Hartley and Davidson,2010).

7.References:

Terradat UK Limited (2014) Electrical resistivity tomography [online] Available at: http://terradat.co.uk/survey-methods/resistivity-tomography/ [Accessed: 13/12/16]

Exploration Instruments LLC (2016) Electromagnetic Geonics EM-31 [online] Available at: http://www.expins.com/item/geonics-em-31 [Accessed:13/12/16]

Reynolds International (2011) EM-31 electro-magnetic ground conductivity mapping [online] Available at: http://www.reynolds-international.co.uk/uploads/files/04tssem31.pdf [Accessed:13/12/16]

https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/297676/scho0309bpqm-e-e.pdf