I do not understand your question well Gayatri Sahu.

It is not clear if are you talking about heavy metals concentration in soil or heavy metals concentration in leachate. The pH of soil has nothing to do with solubility of heavy metals in solid soil.

Please specify your question in more detailde.

Best regards

Vit

Hi Gayatri,

As you have already stated that you sampling site is an dumping place. I think the heavy metals in soil comes from dumping materials. Here soil pH nothing has to do with heavy metals in regards of your question.

Regards,

Sandeep

Hi Gayatri,

as the collegues mentioned, the heavy metals may exist in the investigated material as complexes and so they may be soluble despite of a high pH. And as David Sutton said, the solubility in the material without treatment has nothing to do with solubility in a procedure of extraktion by addition of acids.

Kind regards, Rolf Naeveke

Since your sampling nodes are ex-damping area such situation is to be expected. Soils have received very high heavy metals exceeding soil's adsorption capacity depending on the excessive damping materials. Therefore nothing to do with soil pH. The other point is your soils could have coarse texture. You also use specific limits for the method in question. Beacause each method is to extract different amounts of heavy metals.

This is compartmentalization. I hope Mganga's input makes the problem clearer for the questioner to move forward.

If "the available heavy metal content" means the heavy metals concentration in leachate, than their concentration may be higher that soil's total absorption capacity or the soil texture may favor their leaching. If "the available heavy metal content" was obtained through acid digestion for AAS analysis, then is normal to have higher concentration than expected.

Heavy metals present in soil irrespective of pH. It availability to plant depends on pH. The soil is alkaline but for extraction we use different solution. If you tell us about extraction method we can say something.

You Extracted soil sample with EDTA, DTPA, Mehich-III, aqua rejia or other?

Metals can also become soluble if the soil redox potential becomes low due to waterlogging. The then the oxygen levels become low and anaerobic microbes shift to using other compounds as the electron acceptor for their metabolic processes. As most of the answers above state you need to be able to distinguish between total metal concentrations and the soluble ones.

i agree with Nafees sir

Metals can become soluble at high pH either by chelating organic matter especially of low molecular weight or low redox potential in waterlogged conditions (for Mn and Fe).

Heavy metals consist of metalic elements usually the transition elements in periodic table with a specific gravity over 5 g/cm3. The behaviour of these elements can be different at changing pH due to complexation reactions with anions and organic fractions. You should individually concentrate on each element in question. You can look up "the chemical equilibria in soils by W.L. Lindsay, 1979 and 2001" you will find very useful information in those books.

Yes, dumps are an accumulation of materials from diverse sources, usually covered up by a thin veneer of topsoil. The chemical composition depends primarily on what is dumped there until sufficient time has passed for weathering and leaching to commence the redistribution of some of the chemical constituents. It cannot be considered as a soil profile that is in equilibrium with its environment. The available evidence suggests that it can take centuries for some of the constituents to reach a steady state equilibrium with the new micro-environment. The chemical reactions involved will essentially depend on both the micro-environment (particularly the climate and moisture regime) and the chemicals that were placed in the dump.

Stuart.

For cationic heavy metals (metalloids) increase of soil pH can decreases metal mobility (bioavailability), by the elevated negative charge of soil colloids, but any soil has a max capacity to immobilized heavy metal ions. At the elevated level of heavy metal concentration, soil pH effects on metal mobility decreases and other factors such as precipitation can affect metal behaviors. You can check the total concentration of metal in soil and its pools (sequential extraction) for evaluation of labile pools of metal.

The immobilization will occur when heavy metals under the relatively higher pH, so there were some traces you could find. It's logically. And,not all type of metals would get mobility when pH increased.

Please clarify the question with thanks

Its mean you have external sourse for heavy metals supply such as irrigation water or pollution by wastewater and you cab insure that by matching mineralogical composition of soil parent material and soil solution composition. In the other hand you need to analyse organic matter content and its element content..

Hope thats helps.

Regards

The nature of metal-bearing phases and, more generally, mineralogy strongly influences metal availability.

So I will suggest you to study the mineralogy of soil and the localisation of metal bearing phases (TEM-EDX and XRD).

For more information about your question I'm sending you some references;

Echevarria G, Massoura T, Sterckeman T, Morel JL (2006)

Assessment and control of the bioavalability of nickel in

soils. Environ Toxicol Chem 25:643–651;

Bani A, Echevarria G, Montarges-Pelletier E, Gjoka F, Sulce S, Morel JL (2014) Pedogenesis and nickel biogeochemistry in a typical Albanian ultramafic toposequence. Environ Monit Assess 186:4431–4442 doi: 10.1007/s10661-014-3709-6;

Massoura, S. T., Echevarria, G., Becquer, T., Ghanbaja, J.,

Leclerc-Cessac, E., & Morel, J. L. (2006). Nickel bearing

phases and availability in natural and anthropogenic soils.

Geoderma, 136, 28–37.