Effects of Bioavailability and Accumulation of Single Metal and Mixture Metal on Toxicity to the Mite, Oppia nitens
Date
2019-10-17
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
0000-0003-2667-3396
Type
Thesis
Degree Level
Doctoral
Abstract
Canada has some of the largest metal deposits in the world and the Canadian mining industry is one the largest employers of labour in Canada. Consequently, mining and smelting operations in Canada are one of the sources of metal level increase in the environment. Metals pollute the terrestrial environment because of fall-out from the mining industry. Soils are major sinks for metals in the terrestrial environment. It is therefore important that metal risk assessment should clearly reflect the metal contamination in the soils.
The main objectives of this thesis were to generate more realistic metal toxicity data using a native Canadian invertebrate species that will help improve metal risk assessment in Canada. Firstly, toxicity of common metals (Cu, Pb, Zn, Co, Ni) found in contaminated sites in Canada was assessed on an oribatid mite, Oppia nitens which is abundant in Canadian soils. The metal toxicities were assessed as singles and as mixtures in five different soils. The metal mixture ratios were fixed such that it reflected ratios of metals found in contaminated sites. The patterns of sensitivity of the mite to metals by soils differed between single metals and metal mixtures. Nickel, which had not been tested with Oppia nitens before, was found to be the most toxic metal to the mite and zinc was less toxic. Concentration addition was protective of 53% of metal mixture toxicity due to antagonistic and concentration addition. Bioavailable metals existed as metals bound to fulvic acid.
After determining the toxicity of the metals in the five soils, the multigenerational effect of one of the metals on soil mites was investigated in the most sensitive soil to single metal contamination. Continuous and pulse zinc exposure effect on O. nitens populations was assessed in three generations of the mites. Using critical-effect levels (EC50s), pulse exposed mites seemed to be tolerant and the continuous exposed mites were sensitive. However, the instantaneous population growth rate showed that both pulse and continuous exposures were more sensitive than their parents. The major finding from this study was that persistence of metals in soils can cause multigenerational adverse effects on continuously exposed mites in the soil.
The last chapter of this thesis investigated the direct effect of soil habitat quality as a site-specific feature on organisms and how it influenced their response to metal contamination. For this test, forty-seven (47) soils were ranked according to their habitat qualities from one to three (high to low), using standard soil invertebrate species (Folsomia candida, Enchytraeus crypticus) fitness and plant (Elymus lanceolatus) productivity as metrics to choose habitat qualities. From the ranked 47 soils, eighteen (18) soils comprising six soils making each habitat quality was chosen in a duplicated experiment. The soils were spiked with increasing concentrations of Zn and the Zn toxicokinetics, toxicodynamics, survival and reproduction of mites were assessed. The mites in the soils of high habitat quality were less stressed than mites in the low habitat quality soils despite being exposed to the same amount of bioavailable metals. The key findings from this study were that soil habitat quality has a direct influence on how its inhabitants cope with metal stress. Therefore, habitat qualities of soils can be considered as a site-specific feature in remediation of contaminated sites.
Description
Keywords
Oppia nitens, Metals, Bioavailability, Multigeneration, Habitat quality, Soils
Citation
Degree
Doctor of Philosophy (Ph.D.)
Department
Toxicology Centre
Program
Toxicology