Cadmium in New Zealand agricultural soils

I summarised cadmium concentrations from soil samples collected by the fertiliser industry between 2006 and 2015, and from soil samples collected by regional councils. Using these data, a statistical model was used to estimate soil cadmium concentrations on agricultural land within each territorial authority. Across New Zealand, most territorial authorities (56 of 66), including all the South Island, had mean soil cadmium concentrations below 0.6 mg Cd/kg.

The highest mean soil cadmium values on agricultural land were in the Otorohanga and Matamata-Piako districts (0.90 and 0.89 mg Cd/kg, respectively). In these districts, around 1% of properties were estimated to have mean soil cadmium in excess of 1.8 mg Cd/kg. The fertiliser industry requires that cadmium concentrations in phosphate fertiliser are below a voluntary limit of 280 mg/kg P. The mean cadmium concentration in fertiliser samples taken between 2003 and 2015 was 184 mg Cd/kg P, 66% of the voluntary limit.