Mean contents of As and heavy metals in the top 20 cm soils of three sampling sites during the whole sampling period (mg kg⁻¹ dry weight).

a,b<p> different letters represent significant differences between three seasons at each site.</p>1,2<p> different numbers represent significant differences between three sites in each season.</p><p>* National Standard of P.R. China <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0107738#pone.0107738-National1" target="_blank">[37]</a>.</p>†<p> SQGs: Sediment Quality Guidelines for marine ecosystem; TEL: threshold effect level; PEL: probable effect level <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0107738#pone.0107738-Han1" target="_blank">[23]</a>.</p><p>Mean contents of As and heavy metals in the top 20 cm soils of three sampling sites during the whole sampling period (mg kg⁻¹ dry weight).