The Single and Combined Effects of Wildfire Runoff and Sediment‐Bound Copper on the Freshwater Amphipod Hyalella azteca

Abstract

The frequency of wildfire is expected to increase with time as a function of climate change. Recent studies in our laboratory have demonstrated that pyrogenic polycyclic aromatic hydrocarbons can cause greater-than-additive effects in Hyalella azteca in the presence of low concentrations of Cu. We hypothesized that freshwater animals inhabiting Cu-contaminated sites, such as those in the vicinity of Cu mines, may be vulnerable to nonadditive toxicity from contaminants released by wildfires. To investigate the interaction between Cu and water conditioned by burnt wood ash (fire extract), we exposed H. azteca for 14 d to binary mixtures of 225 mg/kg Cu-enriched artificial sediment (225 mg Cu/kg) and a fire extract dilution series (12.5, 25, 50, 75, and 100%). All binary mixtures of Cu-enriched sediment and fire extract resulted in complete mortality with the exception of Cu-enriched sediment + 12.5% fire extract. The combination of Cu-enriched sediment with 12.5% fire extract had a more-than-additive effect on survival and tissue Cu concentration, but there was no reduction in growth or acetylcholinesterase activity compared to the 225 mg/kg Cu-contaminated sediment or fire extract control, respectively. Acetylcholinesterase activity was significantly reduced in amphipods exposed to fire extract, but the presence of Cu did not exacerbate this effect. The results suggest that Cu-contaminated water bodies that receive runoff from wildfires are at risk of enhanced toxicity.

Fire and rain: A systematic review of the impacts of wildfire and associated runoff on aquatic fauna

“…Although acute exposure to extracts of wildfire–runoff do not appear to cause mortality to aquatic taxa, PAHs and metallic constituents can accumulate in tissues and have been associated with oxidative and neuronal stress (Nunes et al, 2017; Plomp et al, 2020; Pradhan et al, 2020). Metals (mainly mercury accumulation has been investigated) and PAHs can accumulate at high concentrations in specific organs (mostly, the guts, gills, and liver) of aquatic animals (Bandowe et al, 2014; Garcia & Carignan, 2005; Plomp et al, 2020). Mean tissue concentrations of copper (Cu) were four times greater in the freshwater amphipod, Hyalella azteca , exposed to aqueous extract of ash compared to controls (Plomp et al, 2020).…”

“…Metals (mainly mercury accumulation has been investigated) and PAHs can accumulate at high concentrations in specific organs (mostly, the guts, gills, and liver) of aquatic animals (Bandowe et al, 2014; Garcia & Carignan, 2005; Plomp et al, 2020). Mean tissue concentrations of copper (Cu) were four times greater in the freshwater amphipod, Hyalella azteca , exposed to aqueous extract of ash compared to controls (Plomp et al, 2020). However, investigation is needed to understand how PAHs and metal accumulation impacts the function of affected tissues, and whether tissue accumulation impair whole‐animal functioning and performance.…”

“…Mean tissue concentrations of copper (Cu) were four times greater in the freshwater amphipod, Hyalella azteca, exposed to aqueous extract of ash compared to controls (Plomp et al, 2020). However, investigation is needed to understand how PAHs and metal accumulation impacts the function of affected tissues, and whether tissue accumulation impair whole-animal functioning and performance.…”

“…For instance, following a major wildfire, salmonid fishes were found to reside at equal densities in fire‐affected and reference sites of Scott Creek, California, but individuals residing in fire‐affected reaches suffered significant loss of physiological condition (as indicated by mass and length estimates) and lost mass in the summer following the fire disturbance (Beakes et al, 2014). Similarly, the survival of freshwater amphipods, Hyalella azteca , was unaffected by wildfire ash, but investigations into oxidative enzyme biomarkers revealed significant oxidative stress (Plomp et al, 2020). The use of physiological tools can provide key insight into the sublethal impacts of wildfires and allow for an understanding of how aquatic animals respond to and recover from wildfire disturbances, though their utility to conservation and management has yet to be realized.…”

Polycyclic aromatic hydrocarbons in terrestrial and aquatic environments following wildfire: a review

“…In addition, fire suppressants and retardants are used to control wildfires, including chemicals such as ammonium phosphate and ammonium polyphosphate. The cumulative and synergistic effects of these chemicals and stressors may be much more severe than increases in PAHs alone (e.g., Plomp et al, 2020), and as such, this requires much more assessment.…”