Theme: 08. Metals

Topic Area: 8c. Precipitation and Stabilization of Metals

Formatted Title:

Sediment pH and Redox Profile Shift in Response to an Electromagnetic Treatment Affecting Metal Speciation, Mobility, and Bioavailability in Treated Bodies of Water

Background/Objectives:

Background. Metal contamination in freshwater environments is an area of concern within the environmental sector. Increased deposition into freshwater sediments – via industrial or anthropogenic sources – can have negative ecological consequences on the health and functioning of freshwater (FW) systems. Altering redox conditions of the sediment environment – via changes in oxygen concentrations or pH – can potentially mediate harmful metal species (e.g., arsenic, copper). Increasing oxygen delivery into the sediment can increase aerobic respiration rates, altering the chemistry of these metal contaminants by reducing their internal loading (i.e., mobility) into the water column or speciation to a less toxic form.

Approach/Activities:

Approach/Activities. Previous research has demonstrated that emitting a low electromagnetic (EM) signal into a variety of FW systems increased oxygen transfer into the water column via air-water interface – up to double the amount in any given system. In collaboration with E M Fluids, Toronto Metropolitan University measured dissolved oxygen, redox potential, and pH profiles of sediment in two aquaria over a 5-week period: one equipped with an EM transducer, and a second that served as a reference.

Results/Lessons Learned:

Result/Lessons Learned. Respiration rates were calculated from oxygen profiles and found that respiration increased as a function of EM treatment, without a change in the thickness of the oxic layer, suggesting a higher rate of oxygen delivery to sediments supporting higher aerobic metabolism. Additionally, profiles show an increase in pH in sediment, particularly near the surface, after treatment commenced: this shift was ~0.8-0.9 pH units near the surface, and ~0.4 pH units at a depth of 1.6 cm. Redox profiles suggest an increase in redox after EMF treatment commenced, although after three weeks, redox was similar in the two aquaria; EM treatment may have supported oxidation of reduced chemical species and accelerated a shift in redox, whereas the reference aquarium experienced a lag. The effects of EMF treatment on redox and pH have implications for speciation of metals, and therefore environmental behaviours of metals in sediments. Application of this system can be used to mitigate metal toxicity in a variety of FW environments including tailings ponds, eutrophic systems, wetlands, an agriculture.

Preveen Varathan

Affiliation

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Sediment pH and Redox Profile Shift in Response to an Electromagnetic Treatment Affecting Metal Speciation, Mobility, and Bioavailability in Treated Bodies of Water