Examining waterborne and dietborne routes of exposure and their contribution to biological response patterns in fathead minnow (Pimephales promelas)

The objectives of the current study were: (i) to gain a better understanding of the relative importance of water and diet as routes of exposure causing toxicity in fathead minnow (FHM) exposed to metal mining effluents (MME) using a full factorial water/food experimental design (Experiment 1), and (ii) to assess differences in the effects of food quality on toxicity by comparing FHM fed both a live and frozen diet of Chironomus dilutus (Experiment 2). The results showed significant increases in general water quality parameters (e.g., hardness, conductivity) and various metals in the effluent treatment waters compared to control waters, with maximum increase seen in the multi-trophic streams. Metals accumulation (Rb, Al, Se, Sr, Tl, Ce, Co, Cu, Pb) effects of both waterborne and multi-trophic exposures were significant in one or more fathead minnow tissue type (muscle, gonads, liver, larvae) relative to those in the control systems. Condition factor and liver somatic index (LSI) of FHM were also significantly affected in both exposures by one or both routes of exposure (water and/or diet). In addition, cumulative total egg production and cumulative spawning events were significantly affected by both waterborne and dietborne exposures, with maximum effect found in the multi-trophic streams. These results suggest that under environmentally relevant exposure conditions, trophic transfer of metals may lead to greater reproductive effects and increased metal toxicity in fish. It also indicates that metals are assimilated in tissues differently depending on the quality of the food (live vs. frozen). Overall, it appears that the multi-trophic bioassay provides an important link between the laboratory and field, which may allow for a more realistic assessment of the true impact of MME's in the environment.

► Objective (i) was achieved by isolating each route of exposure (diet, water and the combination of the two) and comparing it to a control.
► The metal mining effluent studied encompassed several different effluent types including: mine water, mill facility, tailing impoundment, treatment pond, treatment facility, seepage and surface drainage effluent.
► Experiment 1 examined exposure pathways by isolating effluent exposure through the diet, water or the combination of the two.
► Experiment 2 examined whether differences in Fathead minnow responses occurred when fish were fed a live or frozen (dead) diet of chironomids.
► Multiple trophic levels (consumers and carnivores) were placed in each artificial stream simultaneously.
► Primary route of exposure to Fathead minnow when held in control water and fed effluent-exposed chironomid larvae.