Heavy Metal/Potentially Toxic Elements

Applications of biosolids are managed to ensure there are no adverse effects to the soil. Soil samples are taken prior to all applications. Biosolids are applied to the soil at a pH between 5.5 and 7.5, which is consistent with productive agricultural soils in the UK. Much of the UK’s heavy industry has now disappeared and so there has been a very large reduction in the form of heavy metal pollution. Heavy metals are also known as potentially toxic elements or PTEs. The amounts of heavy metal present in biosolids have reduced due to strict environmental regulations. Mineral phosphate fertilisers contain 75% more cadmium than biosolids because cadmium and phosphates are mined from the same rock. Fertilisers now average 40mg Cd/kg P2O5, whilst the concentration in biosolids would be 23 mg Cd/kg P2O5. Due to a reduction in heavy metal inputs at source, the concentrations found in biosolids has been very successfully reduced. Levels of cadmium and lead in particular have been dramatically reduced. (see graph below).

 Application of Biosolids