Soil pollution by chemical substances often stems from an accumulation of persistent, i.e., non- or not readily degradable, pollutants. Persistent pollutants include in particular heavy metals and their compounds as well as several groups of organic pollutants.
These pollutants end up in or on soil via different routes, including for example atmospheric inputs from transport and industry, inputs from agricultural land use, introduction to soil in the recovery of materials of all kinds, and earth moving work. Mud moved by flooding can also be a source of pollutants.
In addition, every private owner or every user of a property can contribute to soil pollution, for example when there are old, defective sewer pipe systems or cesspits on the property or when biocides are used and improper fertilization practices are applied in allotment gardens.
When do pollutants lead to hazards?
Limit values provide the answer to this question. They are derived using scientific (e.g. ecotoxicological or human-toxicological) methods. Important requirements for the analysis and assessment of pollutants in soil are laid down in the Federal Soil Protection and Contaminated Sites Ordinance (BBodSchV). The Ordinance contains detailed rules for sampling, sample preparation and chemical analysis as well as binding assessment standards. In addition to generally applicable precautionary values, the latter also include trigger and action values for specific pathways and uses.
Precautionary values differentiated by soil type exist for the metals lead, cadmium, chromium, copper, nickel, mercury and zinc and for the organic substances PCB6, benzo(a)pyrene and PAH16. Precautionary values are established on the basis of ecotoxicological effect thresholds and compared with rural background concentrations. They contain a safety margin in regard to the hazard-based trigger values. Where precautionary values are exceeded, the additional input of pollutants via all pathways must be limited to a maximum permissible load. There is concern that adverse effects may occur.
The precautionary values are applied, for example, where materials (mainly soil material, sewage sludge, biowaste) are applied onto or introduced into the soil as well as in the permitting of new industrial installations. They can also be used as targets for the cleanup of contaminated soil. To prevent an accumulation of pollutants from agricultural use, the soil protection requirements for the application of sewage sludge (Sewage Sludge Ordinance, AbfKlärV), liquid manure and fertilizers must be updated. Advising on needs-based use of fertilizers (Fertilisation Act, DüngG) and pesticides (Plant Protection Act, PflSchG) is being stepped up and financial incentives are being created with a view to minimizing harmful effects.
Additionally, the urgency and effectiveness of measures to reduce substance inputs can be evaluated throughout Germany by means of “critical loads”. Critical loads are area-related thresholds for pollutant input and take land use into account. Where critical loads are complied with, significant harmful effects on the ecosystem concerned are not expected to occur according to present knowledge.
