Science Current Event Summary-4

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Purpose:

Knowing how to modify soil composition is always important in gardening and agriculture because even subtle changes in soil chemistry can do such things as cause the crop to grow immensely more healthily or cause it to put all its energy into growth and neglect producing fruit. The purpose here was to find soil mixes that affect levels of Copper (Cu), Chromium (Cr) and Arsenic (As).


Hypothesis:

No hypothesis was mentioned in the abstract; it seems as if the researcher(s) involved simply conducted the experiment and collected data.

Procedure:

Set up nine samples of soil that have been contaminated with "chromated copper arsenate". Incorporate different substances into said samples and observe how the CCA levels change. Data was collected using sequential extraction and "modified solvent" extraction (I believe that the latter method is the one that was used to determine levels of Phosphorus (P), Nitrogen (N) and Potassium (K) in the project I conducted last year). Some soils used were peat, kaolinite, and highly organic or mineral mixes. The abstract does not establish what the nine samples were specifically.


Results:

Peat seemed to have a very strong influence (whether positive or negative was unestablished), kaoline seemed to have very little effect, and mineral soils seemed to retain very little of the three metals, whereas organic soils seemed to retain large amounts.

Conclusion:

In more mineral soils, copper and chromium see to be more available to plants for use, making it healthier, but organic soils seem to have more conducive levels of arsenic. Also, in organic soils, some reduction occurred, modifying arsenate to form arsenite.

Questions:

1. Which of the three metals mentioned is thought to be most critical to the health of plants?
2. What inspired this project?
3. Is there a way to more naturally produce a soil that has the most desirable levels of the three metals?

Sources:

Balasoiu, Cristina F., Deschênes, Louise, & Zagury, Gérald J. (2001). Partitioning and speciation of chromium, copper, and arsenic in CCA-contaminated soils: influence of soil composition [Abstract]. Science of the Total Environment, 239-255. Abstract retrieved from http://www.sciencedirect.com/science/article/pii/S0048969701008336.


Pictures: http://www.periodictable.com

Annotated Article: 

This study focused on the influence of soil composition and physicochemical characteristics on the retention and partitioning of Cu, Cr and As in nine chromated copper arsenate (CCA) artificially contaminated soils. A statistical mixture design was used to set up the number of soils and their respective composition. Sequential extraction and modified solvent extraction were used to assess Cu and Cr partitioning and As speciation [As(III) or As(V)]. It was found that peat had a strong influence on CEC (232 meq/100 g), on buffer capacity and on Cu and Cr retention, whereas kaolinite's contribution to the CEC was minor (38 meq/100 g). Average metal retention in mineral soils was low (58% for Cu and 23% for Cr) but increased dramatically in highly organic soils (96% for Cu and 78% for Cr). However, both organic and mineral soils demonstrated a very high sorption of added As (71–81%). Levels of Cu and Cr in a soluble or exchangeable form (F1) in highly organic soils were very low, whereas the levels strongly bound to organic matter were much higher. Conversely, in mineral soils, 47% of Cu and 18% of Cr were found in F1. As a result, Cr and Cu in moderately and highly organic contaminated soils were present in less mobile and less bioavailable forms, whereas in mineral soils, the labile fraction was higher. The modified method used for selective determination of mineral As species in CCA-contaminated soils was found to be quantitative and reliable. Results revealed that arsenic was principally in the pentavalent state. Nevertheless, in organic soils, arsenite was found in significant proportions (average value of 29% in highly organic soils). This indicates that some reduction of arsenate to arsenite occurred since the original species in CCA is As(V).