Biological tests for immobilization of arsenic, cadmium, chromium and lead with chemical amendments: Earthworm, seedling and root morphological endpoints

Micah T Humphreys, Purdue University

Abstract

The work presented in this dissertation encompasses three experiments involving soils contaminated with As, Cd, Cr and Pb. One experiment involved bioassays to determine the toxicity and bioavailability of metals after chemical amendment were added to the soil for immobilizing As, Cd, Cr and Pb. The second experiment considered metal-spiked soil heterogeneously placed in a column of soil and the subsequent effects on maize and wheat root growth. The final study involved maize root growth in two contaminated soils collected from the field with and without addition of ameliorative chemical amendments to stabilize the metals. Three metal-contaminated soils collected from field sites were amended with combinations of manganese, phosphorus and cerium. A sandy soil from a former cadmium paint pigment manufacturing site (NJ soil) was amended, but the amendments increased toxicity to earthworms. Amendments had no effect on barley germination but depressed root growth. When the same amendments were applied to an organic soil from a former smelter site (smelter site soil), earthworm survival improved, earthworms gained biomass, and had reduced metal tissue concentration compared to the unamended smelter site soil. A sandy loam soil with slightly elevated metal levels (UT soil) was amended, and amendment addition caused reduced lettuce root length and significantly elevated Cd earthworm tissue concentration. Maize and wheat plants were grown in a three-layer column of soil where a metal-spiked soil was placed in the middle layer, while control soil was placed in the top and bottom. Maize roots exhibited reduced branching, reduced length and surface area in the middle layer when As or Cd was added, and a slight increase in growth parameters when Pb or Cr were added, compared to the control. The total maize root production was not affected at the whole-column level, and in the case of As and Cd, root morphologic plasticity exhibited avoidance-like behavior. Wheat roots tended to proliferate in the uncontaminated top layer while reducing growth in the middle and bottom layers, exhibiting an avoidance response different than that observed for maize. In a similar study on maize root parameters, smelter site soil and NJ soil were placed in the bottom half of a soil column and given chemical amendments or no amendment, while an uncontaminated soil of a similar texture was placed in the top half. For the NJ soil the addition of amendments caused greater root growth in the bottom layers compared to the unamended NJ soil. Maize root growth was inhibited in the smelter site soil without amendment, while significant proliferation occurred in the uncontaminated top layer of the same treatment. When amendments were added to the bottom layer, root distribution became more balanced between the top and bottom layer, and the avoidance of the bottom layer seen in the unamended smelter site soil was overcome.

Degree

Ph.D.

Advisors

Schwab, Purdue University.

Subject Area

Agronomy|Soil sciences

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