Community effect concentrations as a new concept to easily incorporate community data in environmental effect assessment of complex metal mixtures.

The goal of this study was to incorporate community data into the effect assessment of environmental and regulatory relevant metal mixtures. In this experiment three fixed mixture ratios (Canadian soil quality guideline ratio - CSQG; Agricultural, residential and Loamy ratio - ARL; and Sudbury ratio - SUD) were tested in a natural community microcosm with 11 doses for each mixture ratio. The effect of metal mixtures on the community was measured using the community effect concentration (EC) concept which assumes that as contamination increases, the community similarity between test and control treatments decreases producing a dose response curve allowing the calculation of community effect concentrations. In regulatory mixture ratios (CSQG and ARL) community EC10s were four times higher than regulatory thresholds and current regulation might be overprotective of the microarthropod communities in some soils. For the contaminated site ratio (SUD), the field dose in the contaminated site corresponded to a community EC20 and if metal concentrations were reduced by 1TU, (from 3.1TU to 2.1TU) effects would be below a community EC10. Overall, the community EC concept was successfully applied and has the potential for inclusion in risk assessment schemes as a measure of community response.

Introducing the Adverse Ecosystem Service Pathway as a Tool in Ecological Risk Assessment.

Soils provide numerous ecosystem services (ESs) such as food production and water purification. These ESs result from soil organism interactions and activities, which are supported by the soil physicochemical properties. Risk assessment for this complex system requires understanding the relationships among its components, both in the presence and absence of stressors. To better understand the soil ecosystem and how exposure to potentially toxic elements impact ESs, we developed a quantitative technique, the adverse ecosystem service pathway (AESP) model. We sampled 47 soils across Canada and analyzed them for properties that included pH and cation exchange capacity. We spiked the soils with a metal mixture and measured 15 soil processes representing five ESs. Using a Pearson correlation, we confirmed that proxies of ESs are linked to soil properties. t test results showed that, apart from soil enzyme activities (p > 0.05), the processes underlying ES proxies are significantly reduced in metal-impacted soils. Using soil properties as predictors of ES proxies, we developed AESP models: one for spiked and another for control soils. These models showed adverse effects on ESs in spiked soils, depicted as changes in partial correlation coefficients. The AESP model, therefore, can be an important tool to understand complex ecosystems and improve risk assessment.

Toxicity assessment of metal mixtures to soil enzymes is influenced by metal dosing method.

Metals are present as mixtures in the environment, yet testing such complex mixture poses design and technical challenges. One possible solution is the use of fixed ratios, i.e. rays of increasing metal concentrations. But fixed ratios rays are compromised when soils dosed with metal salts are leached due to metal-soil selectivity rules. Two alternative metal forms, metal oxides and spinel minerals of quinary metal mixtures (Pb, Cu, Co, Ni, Zn), were evaluated for their toxicity to soil microorganisms measured by the activity of ammonia monooxygenases and acid-phosphatases in three soils. Leaching, a required step for salts, had a larger effect on ammonia monooxygenases than metals. Generally, metal salts were the most toxic form, while the spinel minerals were the least toxic form. Two extractants, CaCl2 and DTPA, were evaluated for their ability to link toxicity to metals across all three metal forms. Salt toxicity was closely linked to CaCl2 extractable concentrations but DTPA was the most appropriate for oxides. We strongly recommend combining fixed ratio rays with metal oxides for metal mixture studies, since soil ratios created using oxides were more precise and required less experimental effort compared to salts and spinel minerals. Furthermore, because DTPA and CaCl2 closely tracked the toxicity of more realistic metal forms (i.e. oxides), we recommend that field studies investigating metal mixtures use both DTPA and CaCl2.

Assessment of exposures and potential risks to the US adult population from the leaching of elements from gold and ceramic dental restorations.

Using data from the 2001 to 2004 US National Health and Nutrition Examination Survey (NHANES) on the number and placement of tooth restorations in adults, we quantified daily doses due to leaching of elements from gold (Au) alloy and ceramic restorative materials. The elements with the greatest leaching rates from these materials are often the elements of lowest proportional composition. As a result, exposure due to wear will predominate for those elements of relatively high proportional composition, while exposure due leaching may predominate for elements of relatively low proportional composition. The exposure due to leaching of silver (Ag) and palladium (Pd) from Au alloys exceeded published reference exposure levels (RELs) for these elements when multiple full surface crowns were present. Six or more molar crowns would result in exceeding the REL for Ag, whereas three or more crowns would be necessary to exceed the REL for Pd. For platinum (Pt), the majority of tooth surfaces, beyond just molar crowns, would be necessary to exceed the REL for Pd. Exposures due to leaching of elements from ceramic dental materials were less than published RELs for all components examined here, including having all restorations composed of ceramic.