A baseline survey of potentially toxic elements in the soil of north-west Syria following a decade of conflict

We present the first region-wide chemical survey of soils in NW Syria following more than a decade of ongoing conflict. We sampled the topsoil at 66 sites, typically located in marginal agricultural (orchards, arable) or peri-urban settings, grouped around 21 localities covering the whole area of NW Syria currently under Syrian Opposition control. Samples were analysed in the UK using inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma optical emission spectrometry (ICP-OES). Topsoil total concentrations of potentially toxic elements (previously referred to as "heavy metals") are broadly consistent with pre-war data from Aleppo and recent data from nearby Turkey. Principal Components Analysis (PCA) of associations among the sampling sites identified three groupings. Ni (133.30 +/- 72.12 mg kg-1) and Cr (122.14 +/- 52.25 mg kg-1) exist in all samples at levels in excess of typical European guideline thresholds for agricultural soil. Observed Cd (0.57 +/- 0.93 mg kg-1), Co (23.07 +/- 18.48 mg kg-1) and As (6.65 +/- 4.51 mg kg-1) concentrations are up to three times comparable values from nearby agricultural regions in southern Turkey. Maximum observed values for Cd, As, and Co, which exceed EU thresholds, are concentrated in a corridor around Sarmada to the west of Aleppo which has seen some of the most intense conflict-related impacts. Cu (28.33 +/- 17.11 mg kg-1), Pb (15.65 +/- 10.85 mg kg-1) and Zn (73.64 +/- 40.15 mg kg-1) also observe maxima in the Sarmada corridor, but show a more even distribution across the region, widely at values above comparable regional values for agriculture but below EU threshold concentrations. We interpret the occurrence of Ni-Cr as consistent with intensive agriculture using wastewater-contaminated irrigation and fertilisers. Cd-As-Co and Cu-Pb-Zn are likely anthropogenic and reflect intense pressures of conflict, informal settlement, unregulated industry and untreated wastewater irrigation on a historically agricultural region. The sampling method was designed to capture regional variations from a minimal dataset and it is likely that local topsoil concentrations at specific points of impact (proximal to locations of shelling, industry, effluent release or population) will be considerably higher than those reported here. This study establishes an important baseline reference for further targeted studies to identify and mitigate specific pollution hazards in this region of ongoing, extreme humanitarian and ecological threat. The first regional topsoil sampling campaign since 2011 maps elevated background concentrations of potentially toxic elements in soils across north-west Syria following more than a decade of conflict.