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 different letters represent significant differences between three seasons at each site.1,2 different numbers represent significant differences between three sites in each season.* National Standard of P.R. China [37].† SQGs: Sediment Quality Guidelines for marine ecosystem; TEL: threshold effect level; PEL: probable effect level [23].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).