For example, the maximum allowable limit for USEPA in agricultural soils are very low when compared to Tanzania's maximum allowable limits see figure below. Does this can affect the management strategies because one value can indicate the soil to be polluted while the other still claiming the soil is safe?
Thanks, Looking to your responses.
Marco
Definitely agree with dear Prof C.A. (Kees) Kan
The legal approach does differ between countries. Some follow a (very) strict toxicological approach, others consider what is reasonably achievable in their country. Precisely !
The legal approach does differ between countries. Some follow a (very) strict toxicological approach, others consider what is reasonably achievable in their country. This may lead to different limits, not only for metals but also other substances like insecticides. Another question is, do they strictly enforce compliance with the legal limits?
The differences could be attributed to the variations in geology of the countries, which determine the soil background values of the metals under consideration.
It is a complex topic. The main reasons to establish/enforce such soil limits are to manage risks on the receiving environment (including soil), human/animal health and marketability of the agricultural produces.
Many countries may not even have such limits established let alone enforced hence having such limits is a sensible starting point regardless of being stringent or lenient. Full credit to the Tanzanian authorities to have established such limits.
Soil experts are divided in setting limits on the basis of bioavailability and wider risks.
If the bioavailability approach is taken, the limits can be set much higher than conventional/conservative limits. However, given much of the heavy metal mobility and availability in soils is driven by soil pH (low pH promotes greater mobility), any such limits must be set in association with soil pH. If not, setting limits based on bioavailability alone may become an academic exercise. For the above reason, some countries regulate pH and heavy metal limits together.
Other issues are soil depth to which such limits apply and land use such as soil disturbance.
Undisturbed soils such as long-term pastoral soils can amplify soil accumulation of heavy metals since much of the heavy metals introduced may accumulate in the surface soils. The opposite will apply to the frequently ploughed up soils where heavy metals are mixed in soils resulting in dilution. Consequently, using the regulated limits the farmer managing ploughed soils will have the advantage of loading more heavy metal on an area basis. The farmer managing un-ploughed pasture could plough the soil to comply with the limits to avoid non-compliance or increased plant uptake/livestock ingestion.
From an international trading viewpoint, soil heavy metals can be an issue if such metals are detected in the exported agricultural produces at unacceptable levels to avoid trade sanctions/restrictions.
Ultimately sensible interpretation and the application of scientific information coupled with pragmatism are critical to balance between environmental/economic/health risks and promoting the reuse of waste materials such as biosolids produced from sewage sludge and sustainable use of phosphatic fertilizers derived from rock phosphates both of which could contain many recognized heavy metals.
On the other hand, I am aware many soils which are deficient in essential trace elements such as Zn, Cu, B and Se, hence sustainable soil heavy metal management must consider both positive and negative effects of such heavy metals.
The limits of USEPA are guidelines to follow but it will be different depends on the soil texture and structure. Also on the agricultural practice in the country and the available technology
It depends on the physico-chemical properties of soil-sediment.Accordingly toxicity decides and so the standard.
Kapila Manoj, Hussein Abdel Halim Abdel Halim El Gammal that means is not possible to use one value to decide the pollution status in different countries
Marco Mng’ong’o It is even more complicated; also comparisons on pollution between different areas in the same country might be hard to make, as the natural background may also differ and what you measure is the sum of background levels and pollution caused by human activities.
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