## 3 Results
### Sequential Extractions
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multicolumn{1}{c}{} & \multicolumn{1}{c}{**I Step**} & \multicolumn{1}{c}{**II Step**} & \multicolumn{1}{c}{**III Step**} & \multicolumn{1}{c}{**IV Step**} & \multicolumn{1}{c}{**V Step**} & \multicolumn{1}{c}{**Resolute**} & \multicolumn{1}{c}{**Sum of Fractions**} & \multicolumn{1}{c}{**Total**} \\ \hline \multicolumn{1}{c}{**Station ID**} & \multicolumn{1}{c}{**Depth (m)**} & \multicolumn{5}{c}{**[As] (ppb)**} & \multicolumn{5}{c}{**[As] (ppb)**} \\ \hline \multirow{5}{*}{**S53/1A**} & 0.0–1.0 & 413 & 952 & 134 & 3229 & 2486 & 7310 & 14,524 & 19,210 \\  & 1.0–1.5 & 307 & 827 & 57 & 759 & 3154 & 5578 & 10,682 & 11,886 \\  & 1.5–2.0 & 307 & 1237 & 68 & 1398 & 3689 & 6300 & 12,999 & 15,228 \\  & 2.0–3.0 & 266 & 2375 & 195 & 8790 & 8510 & 19,534 & 39,669 & 44,506 \\  & 3.0–4.0 & 324 & 1701 & 55 & 712 & 7521 & 10,319 & 20,632 & 21,130 \\  & 4.0–5.0 & 672 & 2374 & 79 & 1301 & 12,760 & 8624 & 25,810 & 25,783 \\ \hline \multirow{5}{*}{**S53/1A**} & 0.0–1.0 & 173 & 1028 & 100 & 4944 & 3201 & 6474 & 15,921 & 24,621 \\  & 1.0–1.5 & 388 & 1055 & 141 & 4520 & 1629 & 4514 & 12,246 & 10,111 \\  & 1.5–2.0 & 328 & 1336 & 135 & 5422 & 3001 & 8444 & 18,665 & 20,824 \\  & 2.0–3.0 & 502 & 2368 & 59 & 1633 & 7654 & 16,576 & 28,793 & 27,099 \\  & 3.0–4.0 & 526 & 1548 & 43 & 782 & 7165 & 5178 & 15,242 & 12,943 \\  & 4.0–5.0 & 565 & 2214 & 82 & 1127 & 11,533 & 5171 & 20,691 & 22,230 \\ \hline \multirow{5}{*}{**S53/1B**} & 0.0–1.0 & 301 & 1303 & 125 & 5588 & 2382 & 8632 & 18,301 & 19,492 \\  & 1.0–1.5 & 269 & 974 & 41 & 759 & 2949 & 5414 & 10,405 & 10,177 \\  & 1.5–2.0 & 316 & 1140 & 58 & 752 & 3283 & 5960 & 11,509 & 10,246 \\  & 2.0–3.0 & 354 & 2057 & 184 & 9889 & 5049 & 17,736 & 35,269 & 32,823 \\  & 3.0–4.0 & 417 & 1791 & 96 & 7022 & 5794 & 11,057 & 26,177 & 27,154 \\  & 4.0–5.0 & 485 & 2368 & 73 & 1294 & 10,390 & 8672 & 23,282 & 26,167 \\ \hline \multirow{5}{*}{**S53/1C**} & 0.0–1.0 & 226 & 1815 & 130 & 5426 & 2186 & 7449 & 17,233 & 19,046 \\  & 1.0–1.5 & 217 & 928 & 43 & 756 & 2233 & 4585 & 8761 & 8689 \\  & 1.5–2.0 & 294 & 1172 & 65 & 1338 & 2674 & 4097 & 9640 & 9638 \\  & 2.0–3.0 & 324 & 1339 & 95 & 8755 & 3028 & 17,542 & 31,083 & 28,935 \\  & 3.0–4.0 & 466 & 1800 & 44 & 789 & 6058 & 7937 & 17,094 & 18,578 \\  & 4.0–5.0 & 550 & 2525 & 69 & 1480 & 12,531 & 7181 & 24,337 & 21,012 \\ \hline \multirow{5}{*}{**S53/1D**} & 0.0–1.0 & 186 & 1713 & 89 & 5960 & 3247 & 6576 & 17,771 & 17,285 \\  & 1.0–1.5 & 219 & 1185 & 120 & 9346 & 2262 & 13,686 & 26,818 & 24,620 \\  & 1.5–2.0 & 308 & 1585 & 195 & 8208 & 3174 & 17,730 & 31,200 & 26,891 \\  & 2.0–3.0 & 409 & 1955 & 49 & 2293 & 7046 & 15,728 & 27,479 & 26,992 \\  & 3.0–4.0 & 424 & 1701 & 55 & 722 & 10,082 & 3705 & 16,689 & 17,343 \\  & 4.0–5.0 & 489 & 2543 & 66 & 953 & 11,745 & 5431 & 21,227 & 21,2 The first As fraction deriving from the sequential extraction consists in the most easily exchangeable and, therefore, the most available species of the metalloid. This fraction represented 2% of extracted As and ranges from 0.7% (core S53/1, depth 2.0-3.0 m) to 3.4% (core S53/1A, depth 3.0-4.0 m) (Table 4). The second As fraction from sequential extractions was an average of 8.5% of extracted As and ranged between 4.3% (core S53/1C 2.0-3.0 m) and 12.2% (core S53/1C 1.5-2.0 m) (Table 4). From the third step onwards, extraction conditions were made severe by using strongly acid or alkaline extracting solutions. In particular in the third step HCl 0.1 M solution was used and this fraction was the less abundant (on average 0.5% of extracted As, Table 4). As extracted in the fourth step of the sequential extraction procedures was on average 16.4% of total As and ranged from 4.3% (core S53/1D, depth 3.0-4.0 m) to 36.9% (core S53/1A, depth 1.0-1.5 m). The soil sample derived from the core S53/1A at the level 1.0-1.5 m was the only sample with an As concentration of the fourth fraction similar to As concentration of the final residue (4520 ppb and 4514 ppb, respectively) (Table 4).