Total concentration (mg kg1) and MgCl2 extractable concentration (mg kg1) of Cd,
Cu, Ni and Zn, electrical conductivity and acidity in non-irrigated biosolids
(0e10 cm) collected in year 1 and year 3. Error values are standard deviations,
n ¼ 10. Concentrations were compared between years by t-test (* ¼ p < 0.05,
** ¼ p < 0.01).