Surface dispersal, emission source and human health risk assessment of heavy metal(loid)s in an active gas field, Southern Iran

: 1 The presence of heavy metal(loid)s in soils from anthropogenic sources such as activities 2 related to fossil fuel processing area could pose serious threat to the ecosystem and human 3 health. However, risk factors depend on the source, distribution and human interaction with these contaminants and therefore case specific study is needed. In this study, using a geological 5 information system (GIS) and 63 surface soil samples, we fully assessed 190 km 2 area of a 6 developing gas region in southern Iran. Mean concentration of manganese (Mn), zinc (Zn), 7 copper (Cu), lead (Pb), total chromium (Cr), cobalt (Co), arsenic (As) and Cadmium (Cd) was 8 341.24, 129.40, 32.90, 26.85, 16.56, 7.52, 0.67 and 0.63 mg kg -1 , respectively, while As, Pb, 9 Zn and Cd surpassed the local background level. Moreover, soil pollution was also assessed by 10 the contamination factor (CF), geoaccumulation index (I geo ) and ecological risk factor (Er). 11 Accordingly, these soils were classified as moderate to heavily polluted with As and Cd and 12 un-polluted to slightly polluted by Cu, Zn, Pb, Mn, Cr and Co. The GIS and soil collection 13 point tracing showed that the natural gas processing and residential activities were both 14 significant pollution sources where ingestion was the main contributor to heavy metal(loid)s 15 uptake. Overall, the hazardous index for noncarcinogenic health impact was < 1 indicating no 16 risk; however, children were at greater risk than the adult. Total carcinogenic risk (TCR) index 17 from As exceeded the maximum tolerable level (1.0E-04) for children and adults. Chromium 18 Co, Cd and Pb exposure were within the acceptable limit in the adult group (TCR < 1.0E-06), 19 but the Pb and Cr health-hazardous indices were higher than guideline value indicating the 20 potential of cancer risk in children. Therefore, remedial actions are required to eliminate or reduce the toxicity of As, Cr and Pb attributed to the impacted soil.


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Extensive release of contaminants into the environment in process of rapid industrial 27 development as well as urbanization is getting worse in recent years and leads to growing 28 public concerns (Mamat et al., 2014;Zhuo et al., 2020). Heavy metal(loid)s (metals and 29 metalloid having densities greater than 5 g/cm 3 ) are typical trace contaminants, which are kidney dysfunction (Järup and Åkesson, 2009;Nawrot et al., 2010). Therefore, knowing the 51 concentration and distribution of heavy metal(loid)s in potentially exposed contaminated soil 52 is critical in controlling and preventing possible adverse health burden. 53 Currently, soil contamination research is extensively focused on determination, 54 distribution, sources and health risks associated with contaminants mostly in the areas with including soil, which needs much attention. 65 Considering the urge of assessing details of potential heavy metal(loid)s pollution in a 66 developing gas field, we studied a 190 km 2 extended gas work zone in Iran -one of the world's 67 largest gas extraction and processing enterprises. The area included two towns and five villages 68 with over 37,000 population. After 40 years of industrial development, it is necessary to 69 examine the soil status as an important environmental indicator in sustainable development and 70 health status. To the best of our knowledge, this study is the first comprehensive assessment of 71 the soil heavy metal(loid) distribution, sources and potential human health risk in the studied 72 area. This study aims to understand the possible contamination characteristics of soil with 73 heavy metal(loid)s potentially linked to natural gas production and processing. This aim was 74 elaborated with the following objectives: (1) to determine heavy metal(loid)s (Mn, Zn, Cu, Pb,  The study area was located between 51°48′E to 52°25′E (longitude) and 27°44′N to 84 28°14′N (latitude) in the south of Bushehr province, Iran (Fig. 1). The study site is semiarid 85 with an annual average temperature of 30.4 °C and relative humidity of 34 -51% during the 86 summer season. The area is 700 m above sea level. The examined prevailing wind direction of 87 the area is northeast to southwest direction, as measured by the Jam Meteorological Office, 88 June 2018. The age of geological formations in the study area varies from Cretaceous to 89 Quaternary but the study area is mainly covered with a unit of the quaternary alluvial plain.

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The gas-related industry spread in a different part of the region with the focus on Jam Gas 91 Refinery in the middle of the studied area. Because of the growing economy, almost 1500 92 vehicles pass daily through the main road from upstream to downstream of the refinery.     (Miller and Miller, 1987). The mineral phases were 112 identified using X-ray diffraction (XRD) for the clay fractions. The patterns were determined 113 on a Philips X-ray diffractometer (a = 1.54 A, 40 kV, 30 mA, calibrated with Si-standard).     Interpolation assumes that if there is less distance between two objects, they have stronger 169 10 similarities, and weak similarities for the farther distance (Carr et al., 2008). In this study, 170 interpolation was run with a weighting power of 2.0 and 12 neighboring samples.  Characteristics of soils in the study region are outlined in Table 1. pH of the study area 179 ranges from 6.1 to 9.81, with a mean of 7.5, suggesting the neutral to weak alkaline. The

Concentrations and spatial distribution of heavy metal(loid)s 210
Mean concentration of heavy metal(loid)s present in Jam area soils ranked as follows with 211 the high to low value Mn > Zn > Cu > Pb > Cr > Co > Cd > As (  who are potentially exposed to these pollutants daily, the applied guidelines could be chosen 232 to a more cautionary threshold, such as that for residential soils to have a better human health   features recorded in the sampling points shows that these points were precinct of rural 287 cultivated land and might have been affected by these activities (Fig. 1 and 2).

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The spatial distributions of Pb elevated in two distinct regions in residential areas, close 289 to cities and around the refinery. A decreasing trend can be recognized by distance from these and 54 were linked to one or many of these potential sources (Fig. 3, Fig. 1). On the other hand, significant effect on the distribution pattern of heavy metal(loid)s ( Fig. 1-3). area is low to moderately polluted (Fig. 4c). The ecological risk factor results are shown in Fig   348   4d. For Pb, Zn, Cr and Cu, the potential low Er indices ( < 40) indicated low risk, while Cd 349 could pose a high ecological risk (Er = 300) and As with Er ≥ 320 could be a very high risk for 350 ecological receptors (Hakanson, 1980 (Table. 2).

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In general, HQ (non-cancer risk) values of the heavy metal(loid)s in the ingestion route 367 of adults were greater than the dermal contact and inhalation (Table. 2). A similar trend, 368 dominant HQingestion, followed by HQdermal and HQinhalation, was also observed for children.

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However, compared to adults, the higher HQ values for children were mostly due to their   indicating that the exposed adults were unlikely to suffer from obvious detrimental health 389 effects (Adimalla, 2020). Compared with adults, HI values of As, Cd, Cr and Pb was less than 390 1 but greater, demonstrating to have a higher probability to experience non-carcinogenic effects 391 than adults in this area for children (Jia et al., 2018;Jiang et al., 2017).

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In addition to non-carcinogenic risk, the carcinogenic health risk (CR) and TCR (total 393 carcinogenic risk) of As, Pb, Cd, Cr and Co were estimated. Carcinogenic slope factors (SFs) 394 are not accessible for all the studied heavy metals; therefore, only for As, Pb and Cd all three 395 pathways were contained for the risk assessment of carcinogenesis while for the other metals 396 only one or two pathway(s) were included in the carcinogenic risk estimation (

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There are no conflicts to declare.