Co-Investigators:
U. Borgmann, Environment Canada, NWRI
Email: uwe.borgmann@ec.gc.ca
Tel. 905-336-6280;

Specific (long term) Objective:

The overall goal of our MITE research is two fold. First, we wish to determine the best methodology for predicting single-metal effects on invertebrates. Measurement of metal concentrations within the animals themselves promises to be a much better predictor of toxic effects than concentrations in the environment, but is not always appropriate for metals which are essential and regulated by animals. Measurement of metal speciation in the water, and modelling of metal uptake and effects based on free ions may be more effective for essential metals. Our second goal is to determine if bioaccumulation and/or speciation can improve our prediction of toxicity in metal mixtures. If one metal affects accumulation of another, it stands to reason that modelling of metal mixture toxicity should be more reliable when based on a body, rather than water, concentration basis.

Objectives for 1998/99:

Our objectives for 1998/99 were to lay the groundwork for more detailed studies if the MITE proposal was accepted by NSERC. One of the main study sites chosen by the MITE network was the Rouyn-Noranda area. We wished to determine if sediments from lakes in this area were toxic to Hyalella azteca, which metals were most bioavailable and most likely to contribute to toxicity, and which lakes might serve as useful field sites for testing bioaccumulation-toxicity-speciation relationships. In preparation for more extensive metal mixture studies we also needed more information on the toxicity and bioaccumulation of nickel in Hyalella. Some data of this type were already available for most other metals (Cd, Cu, Hg, Pb, Tl and Zn). Some preliminary mixture studies were also planned.

Accomplishments to date:

Accomplishments in the current year include development of a methodology for measuring multiple metals in Hyalella using ICP-MS (in collaboration with NLET-EC). The method has been tested on animals exposed to sediments from Sudbury and seems to be reliable. Use of ICP-MS considerably reduces analysis time for multiple metals, including analysis of field samples and tests with metal mixtures.

Chronic toxicity tests were conducted with sediments from 14 lakes (21 samples) in the Rouyan-Noranda area. Sediments from eleven of these lakes were provided by the GSC, including surface sediments and deeper (20-30 cm deep-i.e. pre-contamination?) sediments. Survival ranged from 20-93%, and was below 50% for surface sediments from only two of the lakes (Table 1). Hyalella and overlying water have been digested and are currently being analyzed for metals by ICP-MS for determination of metal bioavailability. This will help identify metals and study sites for future work.

Chronic toxicity and bioaccumulation of nickel to Hyalella have been measured for comparison with similar data for Cd, Cu, Hg, Pb, Tl and Zn, but some of these experiments are currently being repeated to refine our estimates of Ni toxicity. This will form the basis for metal mixture studies including Ni. Estimated critical body concentrations (4-week LBC25s) are around 200 nmol/g dry weight, similar to those for Cd, Hg, Pb and Tl. Values are slightly lower after 24 hr gut clearance; gut clearance is required for experiments with sediments. Data collected so far suggest that body concentrations are much more reliable indicators of toxicity than sediment or water concentrations, in agreement with previous observations with other metals (Table 2).

Preliminary one-week single-metal and Cd-Cu-Ni-Pb-mixture toxicity tests have been conducted. The mixture contained metals at equivalently toxic concentrations, and resulted in 50% mortality at 2.6 times the concentration expected if toxicity was strictly additive on a water concentration basis. Body concentration analyses are currently in progress and should reveal if toxicity is more closely additive on a body concentration basis. These data should provide a basis for designing more detailed chronic toxicity tests.