Environmental contamination following the Grenfell Tower fire.

The Grenfell Tower fire in central London, started within a flat, engulfed the whole 24 storey building in flames, killed 72 people and spread toxic effluent via the plume and particulate deposits. Soil samples from 6 locations up to 1,2 km from the Tower, together with semi-burnt fire debris and char samples, were collected 1 and 6 months after the fire. Additionally, dust samples and condensates were collected from a flat 160 m away from the Tower after 17 months. Samples were analysed for common potentially toxic components of fire effluents and synthetic vitreous fibres. Samples collected within 140 m of the Tower showed, amongst other toxicants, polychlorinated dibenzo-p-dioxin concentrations 60 times greater than UK urban reference soil levels; benzene levels were 40 times greater; levels of 6 key polycyclic aromatic hydrocarbons (PAHs) were approximately 160 times greater. PAHs levels are approximately 20 times greater than those reported from nearby Hyde Park before the fire. To explain the presence of these pyrogenic contaminants char and partially burnt debris were also collected and analysed. Benzene, PAHs, isocyanates and phosphorus flame retardants were found. Hydrogen cyanide and synthetic vitreous fibres were present in both soil and debris. Particulate and pyrogenic contamination in the immediate vicinity is clearly evident, and may have leached out of fire debris, char and dust. Further analysis of the area around the Tower is necessary to understand potential health risks.


Harmful Effects of Fire Effluents
UK National Fire Statistics (2018) show that the acute toxicity of fire effluents is the biggest short-term cause of death and injury from unwanted fires. Large fires produce smoke containing high concentrations of particulates and toxic gases such as, the asphyxiant gases, carbon monoxide (CO), hydrogen cyanide (HCN) and respiratory tract deep lung irritants. As the fire develops, the yields of all products of incomplete combustion including CO, HCN, organic compounds and soot increase -typically by factors of 10 to 50. Molecular toxicants bind to smoke particles (airborne soot and tarry droplets) allowing them to penetrate deep into the lung causing respiratory distress and pulmonary oedema (flooding of the lungs). This is closely followed by incapacitation and death, from few hours to several days or even years after exposure (Stec and Hull 2010;Stec 2017).
There have been surprisingly few reports of the long term consequences of unwanted fires.
Persson and Simonson (1998) showed that in Sweden they contributed around 10% as much as transport-derived particulate emissions. Fires also release a rich cocktail of pollutants, many of them acutely or chronically toxic, including carcinogens such as semi and volatile organic compounds (SVOC/VOCs), PAHs, respiratory sensitizers such as isocyanates from some nitrogen-containing fuels, and persistent, bioaccumulative and toxic compounds such as polychloro-and polybromo dibenzo-p-dioxins and dibenzofurans (PCDD/Fs and PBDD/Fs) and polychlorinated biphenyls (PCBs), formed by burning halogen containing fuels (McGee et al. 2003;Landrigan et al. 2004).
Benzene is a carcinogen in its own right (ATSDR 2018a). Other aromatic SVOC/VOCs are of particular toxicological significance as precursors of PAHs and carcinogens Some PAHs, PCDD/Fs and PBDD/Fs (the most toxic is 2,3,7,8-tetrachlorodibenzodioxin (TCDD)) are also genotoxic and mutagenic (ATSDR 2018b). Benzo(a)pyrene (BaP) was initially identified as the most toxic PAH species, however more recent studies have identified 7,12dimethylbenzo(a)anthracene as having a 20-fold higher toxic equivalence factor (TEF) than its parent compound and twice that of BaP (Andersson and Achten 2015). A study by Wang et al. (2009) showed that PAHs are transformed in the atmosphere or metabolically into hydroxy-PAHs, which are more genotoxic than the parental PAHs. These compounds have been linked to firefighter cancers through the analysis of their exposure (Stec 2018).
The study by Bengtström et al. (2016) showed that isocyanates have been positively identified in fire smoke and are widely used in the manufacture of flexible polyurethane (PU) foams for upholstered furniture and rigid PU or polyisocyanurate (PIR) foams for insulation in buildings.
Isocyanates are respiratory sensitizers that can cause asthma attacks. They also trigger irritant and allergic forms of contact dermatitis (rashes, itching, swelling of extremities etc.) and less frequently hypersensitivity pneumonitis -an inflammation of the alveoli caused by inhaled isocyanate particles. A common decomposition product of isocyanates is methyl isocyanate (MIC) which also causes swelling of the lungs and breathing difficulties.
Studies by Lippmann (2014 and2015) on the aftermath of the World Trade Centre showed that synthetic vitreous fibres (SVF) were one of the most significant health damaging contaminants after the fire. Inhalation exposure to airborne SVFs is a public health concern because like other particulate matter, fibres that are released in fires can be suspended in air (as dust or ash), inhaled and deposited in the lung (ATSDR 2018c). Lippmann (2014) identified the minimum critical fibre lengths for asbestosis (interstitial fibrosis), mesothelioma and lung cancer to be ∼2 μm, ∼5 μm and ∼15 μm, respectively. With regard to fibre diameter for asbestosis and lung cancer, fibres with diameters >0.15 μm appear to be of predominant significance (as thinner fibres can be more readily cleared via the lymphatic system) whilst for mesothelioma (and other lesions of the mesothelium), fibre diameters <0.1 μm seem to be the most pathogenic.

Environmental Pathways
The interaction between a fire and its surroundings or environment proceeds via direct gaseous and particulate emissions to the atmosphere and localised deposition to soil and water. Subsequent dispersion and deposition of atmospheric emissions results in widespread, low level contamination of soil, ground and surface water, as shown Figure 1. Van Loon and Duffy (2000) reported that particles with diameters less than 10 µm will have a deposition rate of around 3 mm s -1 and will tend to remain airborne, travelling with the smoke plume. Particles with diameters greater than 100 µm will have a settling velocity of 0.3 m s -1 and are likely to be deposited close to the fire. The degree to which fire species are partitioned between different phases (gaseous, aqueous, solid etc.) also depends on their physical characteristics and weather conditions (temperature, rain, wind speed etc.). For example, PAHs will agglomerate eventually leading to soot formation. The agglomerating species will initially travel as airborne particulates, but may grow large enough to sediment into water or soil, while CO will remain in the gas phase. Cyanide is released into air as a gas and to a lesser extent as particulate bound cyanides (ATSDR 2006). Cyanide can be transported over long distances before decomposition by reaction with hydroxyl radicals. In soil, HCN co-exists with alkali metal salts where it volatilises or degrades rapidly. Alternatively, HCN may be immobilised into metallo-cyanide complexes such as ferricyanides or ferrocyanides (ATSDR 2006). MIC will only persist in the atmosphere from a few hours to a few days, while in soil it will be broken down into other compounds upon contact with moisture (ATSDR 2014). PAHs and VOCs are comprised of species that partition differently according to their mass, with lighter species remaining primarily in the gaseous phase and heavier species tending to deposit on surface water or soil when absorbed on particulates (>2.5 µm) such as fly ash and soot (Van Loon and Duffy 2000). Humans can also be exposed to PAHs through inhalation or dermal contact with re-suspended soil and dust (Stec et al. 2018). While human-soil contact generally occurs outdoors, inhalation is also identified as a source of PAHs indoors, where people spent 80-93% of their time (WHO 2010).
SVFs with smaller diameters become airborne more readily than fibres with larger diameters.
SVFs remain unchanged in air, soil or sediment over long periods (Bernstein et al. 2005).
The UK's Public Health England (PHE) provides specialist advice on health including health advice on air quality, smoke exposure, asbestos, and the clean-up process (PHE 2018a). The data from the air quality monitoring in the area surrounding Grenfell Tower, since the start of the fire on 14 June, has shown that the risk to people's health from air pollution around the Grenfell Tower site was consistently low. Levels of gas particulate matter (PM 10 ) remained low and monitoring results for dioxins, furans, PCBs and PAHs were broadly equivalent to background levels for London. No asbestos was reported as found, despite being present in the Grenfell tower. There are no reports of contamination measurements being taken from the soil or water run-off. No measurements appear to have been carried out by UK's Environmental Agency or the local authority (the Royal Borough of Kensington and Chelsea (RBKC). RBKC are legally responsible for assessing and quantifying contaminated land within their community (PHE 2018b). The rationale for the current study was to address concerns from the Grenfell community related to the potential soil contamination and establish whether more detailed investigation is required.

Materials and Methods
Two char samples were collected from balconies 50 and 100 m from the Tower 1 month after the fire and analysed (Char1 and Char2). Based on the findings soil samples, together with fallen fire debris and more charred soot samples (Res and Char3) were collected 6 months after the fire at different distances from the Tower. Sampling was limited by locations where there was permission to collect soil and aimed to follow the direction of the prevailing wind at the time of the fire (South Easterly), with location shown in Figure 2a and wind on the day of fire Figure 2b (TimeandDate 2018). 17 months after the fire char from a balcony (Char4), indoor dust and a yellow oily deposit on a vertical fabric window blind (described by the occupier as "contaminated by the fire") were collected from a flat 160 m from the Tower. Table   1 shows the details of the char and soil samples. A standard soil sample, Kettering loam soil, was obtained from Boughton Loam Ltd (containing clay 24%, silt 18%, sand 58%, organic content 6.72%). It is a preferred natural soil used as a standard in contamination analyses.
Quantitative analyses for PCDD/Fs, PAHs, benzene and metals were carried out on the char and soil samples. Gas chromatography-mass spectrometry (GC-MS) was used for SVOC/VOCs. Qualitative screening (thermogravimetric analysis coupled with gas phase Fourier Transform Infrared Spectroscopy, (TGA-FTIR)) was used to check for the presence of common fire effluents on all samples. Finally, the contaminated window blind was extracted and analysed for the presence of isocyanates, in order to characterise the yellow oily deposits.

Sample Collection
Soil samples (approximately 2 kg) were collected from the ground at depths of up to 200 mm.
A fresh pair of gloves was used for each sample collection and the trowel was cleaned before and after each collection. The samples were stored in airtight 1 L dark glass jars covered in aluminium foil and kept at 4°C.
Approximately 60 pieces of what appeared to be char from insulation foam (the largest being 300 mm in width and 460 mm in length, with an approximate density of 18 kg/m 3 ) were collected from the ground within 90 m of the Tower. A semi-burnt piece of fire debris, recognisable as a sheet of insulation material (Res), was also found and collected. Samples were stored in dark polyethylene bags.
Char samples were also collected from three balconies (Char 1, 2 and 4) between 50 and 160 m from the Tower. Dust samples were collected from five different locations within one apartment, 160 m from the Tower, and combined. Two pieces of the window blind, one with visible soot and yellow oily deposits and the other without, were also collected from the same apartment.

Sample preparation
Up to 5 g of each soil sample was then dried to a constant weight on a watch glass in an oven (VWR Dry-Line 115) at 60 °C to determine the moisture content, then sieved (5 mm) and ground to ensure a homogenous sample (the smell of fire smoke was observed for the soil samples 1 to 3). The moisture content, based on triplicate analyses, is reported in Table 1.
Non-dried samples were used for TGA-FTIR analysis in order to avoid volatile losses.  Laboratory blanks were run alongside samples (intervals specified in individual sections 7 below). All water was distilled. All samples were kept at 4 °C in a locked enclosure prior to 8 analysis. All analyses were conducted in the analytical laboratories of the University of Central 9 Lancashire except for the dioxins and furans which were quantified in a private UKAS 10 accredited laboratory. The limits of detection (LOD) and limits of quantification (LOQ) for 11 analysed fire effluents together with the dioxins and furans recoveries can be found in the 12 supplementary material (Tables S1-S8). 13

pH 14
Approximately 20 g of each soil was mixed with 20 mL of deionised water and the water pH 15 measured using a glass electrode in triplicate (Jenway 3540). 16

CHNS analysis 17
Approximately 2 mg of dried sample was placed into a tin capsule and run on a 18 ThermoScientific Flash 2000 CHNS/O analyser (detection sensitivity within ±1%), in order to 19 determine the presence of nitrogen. Each sample was analysed in triplicate with a blank run 20 as part of the initial CHNS calibration daily. The instrument was calibrated with BBOT (2,5-Bis 21 (5-tertbutylbenzoxazol-2-yl) thiopene) (Elemental Microanalysis, B2135) (6.51 N%, 72.53 22 C%, 6.09 H%, 7.44 S%) using the K-factor calibration method. In place of laboratory blanks 23 between samples, BBOT standard was run every 15 samples in order to check the response 24 of the CHNS analyser. 25

ICP-OES screening 26
The method used was based on EPA 6010D (U.S. EPA 2014). 0.1 g of the sample was 27 digested in 10 mL of concentrated nitric acid (Fisherbrand) in a microwave digester (Milestone 28 Ethos EZ SR12) at 200 °C for 45 min. 0.1 mL of the digested sample was added to 9.9 mL of 12 water, which was then analysed by Inductively Coupled Plasma-Optical Emission 30 Spectrometry (Thermo Scientific iCAP 7000 ICP-OES) for elemental composition. Samples 31 were run in quadruplicate with each individual sample tested three times for consistency. The 32 RSD for all final results was less than 5%. Blanks prepared from digested acid were run after 33 every fifteen samples, and were all below the limits of detection (LOD) for all elements 34 analysed. The LOD and LOQ were calculated as three and ten times the standard deviation 35 from the analysis of the standards and the blanks (Table S1). The standards used for 36 comparison were the TraceCERT® 1000 mg/L P in water and the multi-element standard 5 37 TraceCERT® in 10% nitric acid (Sigma Aldrich). run every ten samples. The chromatograms used for analysis were blank subtracted. The LOD 47 was calculated using three times the signal to noise ratio of the analyte, while the LOQ was 48 calculated using ten times the signal to noise ratio. The LOD and LOQ were 0.11 and 49 0.54 ppm respectively. Sigma Aldrich. Laboratory blanks were analysed with every ten samples. The PAHs were 70 quantified using external standard calibrations. The LOD was based on three times the signal-71 to-noise ratio of each analyte (related to the 5g samples) while the LOQ was based on ten 72 times the signal-to-noise ratio, as shown in Table S2. Responses below the LOQ were not 73 included in this analysis. The average blank levels were below the LOD for all PAHs. 74

Polychlorinated dibenzo-p-dioxin and polychlorinated dibenzofuran analysis 75
Quantification of PCDD/Fs was based on EPA1613 (US EPA 1994). The analysis was 76 undertaken in a UKAS accredited laboratory, approved to quantify dioxins. This includes a 77 spiked sample and a reference material analysed alongside the samples on a weekly basis. 78 The LOD and recoveries for each sample are shown in the supplementary document 79 (Table S3- Mixture). The UPLCMS was purged before testing with the UPLCMS grade solvents, and three 98 blanks were run immediately prior to the samples. Due to the low quantity of the samples, they 99 were treated as qualitative samples and the MS spectra compared to spectra obtained from a 100 purchased calibration standard mixture used as a reference. The detailed analytical settings 101 are presented in Table 2. 102  were prepared on carbon stickers which were placed on SEM stubs for the analyses. 127

ICP-OES analysis 129
Aluminium, zinc, copper, lead and other metals were present in soil within UK Environment 130 Agency baseline pollutant levels in soil (EA 2007a). Phosphorus, occurring naturally in the 131 soil, was present at higher levels for soils S1-S3 collected near the Tower (within the range of 132 140-170 mg/kg) than for S4 to S7 with values between 85 and 35 mg/kg, respectively.    Tris(chloroisopropyl) phosphate (TCPP), tris(2-ethylhexyl) phosphate (TEHP) and tricresyl 155 phosphate (TCP) were identified in samples S1 and S2, fire debris and Char3. These are 156 commonly used in insulation foam and upholstered furniture foam and do not occur naturally 157 in the soil (Hewitt et al. 2017).  Figure 4b shows the HCN profile of the iron 174 cyanide complexes alongside S1 to S7.

Synthetic Vitreous Fibres analysis 178
SVFs were identified and isolated from soil samples S1 and S2 and were found attached to   total sum of 6 PAH concentrations (S1), 45 m away from the Tower, is approximately 20 times 213 higher than that reported in Hyde Park (or approximately 160 times greater than the reference 214 soil). S2 to S4 exceeded these reference values by factors between 40 and 60. S5 to S7 are 215 comparable to the reference soils. PCDD levels are around a factor of 70 greater than those 216 collected in Hyde Park or a factor of 60 greater than the UK urban reference soil values. S4 217 contains lower concentrations than S1 to S3, but these are still three times higher than the UK 218 urban or Hyde Park concentrations. 219 Seventeen 2,3,7,8-substituted PCDD and PCDF congeners (Table 3)  and Cancer Risk (CR corresponding to a 10 -6 risk level for carcinogens) are presented in Table  227 5. Reference doses, slope factors and other parameters for estimating human non-cancer and 228 cancer risks were taken from Regional Screening Levels Tables and EPA equations (U. S. 229 EPA 1989;1991;2001;2009;. In this study, the body weight was chosen 70 kg for The Hazard Quotient (HQ) together with the lifetime cancer risk was calculated and is 237 presented in Table 5 nearest to the Tower. This corresponds to an increased risk of any adverse health effects 248 from PAHs, but not from dioxins and furans. The table also shows the cancer risk to humans 249 multiplied by a factor of 10 6 . Values exceeding 1 x 10 6 indicate an increased cancer risk. These 250 are also shown in bold in Table 5. The four soil samples (S1-S4) closest to the Tower indicate 251 significantly increased cancer risk from dioxin and furans, as well as for PAHs, via dermal 252 intake.  The elevated levels of dioxins and furans and PAHs found in soil samples is in stark contrast 268 to the undetectable levels found during air monitoring by PHE (PHE 2018a). This is 269 unsurprising since any gas phase PAHs or PCDD/Fs will have been dispersed prior to 270 commenced of the PHE analysis (month after the fire) (PHE. 2018b). 271 The HCN evolution from the soil, mirrors the temperature range of release from ferri-and ferro-272 cyanides. This suggests that S1 to S4 were exposed to significant quantities of HCN, blind that was exposed to the outside air, is an obvious health concern particularly as it was 278 found 17 months after the fire within a living space. 279 Analysis of the SVFs from the three insulation panels (PIR, PhF, SW) used on the Tower was 280 compared to that of the SVFs found in soil, char and residue (see section 3.8). It was found 281 that SVFs isolated from the soils are more likely to originate from PIR for S1 and PhF for S2. 282  The data needs to be interpreted with caution as soil is a complex matrix which can vary 290 significantly, even within a small area such as the Grenfell environments. A much more 291 valuable study could have been undertaken in the immediate aftermath after the fire. The 292 absorption and release of toxicants will depend both on their chemical nature and the 293 characteristics of the soil. Sampling from better controlled environments such as plant pots, 294 where a known potting compost has been used and the medium has been undisturbed since 295 the fire, have potential to identify fire contaminants more reliably. In addition, indoor 296 contaminants resulting from deposits within residents homes (dust) have greater potential for 297 positive identification and establishing their relationship to any long-term health effects. 298 From earlier study on the fire behaviour of façade materials, it has been found that brominated 299 flame retardants were not present in significant quantities on the exterior face of the building 300 presence and should be quantified in any follow-up study. 311 Any health effects, together with long-term fire exposure monitoring, should also be carried 312 out and supervised by a multidisciplinary team with medical, environmental, fire and 313 combustion toxicology expertise. Public agencies need to be adequately prepared to provide 314 reliable guidance to the public on more appropriate means of exposure assessment, risk 315 assessment, and preventive measures -in the event of a recurrence such as this tragic fire. 316

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This work was supported by the Faculty of Science and Technology at University of Central 318 Lancashire. 319