Topsoil composite samples were collected in the study area at a
depth of 0–10 cm, with foreign objects removed. At each point, three
composite samples were obtained. Topsoils were kept in plastic bags,
and once in the laboratory they were oven-dried at 40 °C for 24 h. All
samples were sieved to b2 mm(using a polyethylene sieve) and stored
in darkness until analytical procedures were carried out (Bäckström
et al., 2004).