ACTIONS AND INTERACTIONS OF TEMPERATURE, pH AND PHOTOPERIOD ON MERCURY BIOACCUMULATION BY NYMPHS OF THE BURROWING MAYFLY HEXAGENIA RIGIDA, FROM THE SEDIMENT CONTAMINATION SOURCE

Abstract

Based on a three‐compartment system — water, natural sediment, Hexagenia rigida nymphs — an experimental study was set up, using a complete factorial design, to quantify the actions and interactions of three abiotic factors (temperature: 10, 18, and 26°C; photoperiod: 6, 12, and 18 h per day; pH: 5.0 and 7.5) on inorganic mercury (HgCl2) and methylmercury (CH3HgCl) bioaccumulation by Hexagema rigida (whole organism and gills). The two chemical forms of the metal were initially introduced into the sediment; the exposure duration was 15 d. Total Hg burdens measured at the whole‐organism level revealed a very high bioaccumulation capacity of this burrowing mayfly species and important differences between the two contamination conditions of the sediment source, a factor close to 20 observed in favor of methylmercury, for similar exposure conditions. Among the three abiotic factors taken into account, temperature and water‐column pH played an important role on Hg bioaccumulated by the nymphs, when considered in isolation and in interaction. An increase in temperature from 10 to 26°C gave rise to an increase in Hg bioaccumulation, with the higher differences close to a factor of 1.7. On the other hand, acidification of the water column from 7.5 to 5.0 led to a decrease in the amounts of the metal accumulated by Hexagenia rigida. These effects were similar for the two Hg compounds, but they were more pronounced when the experimental units were contaminated by methylmercury. This comparative analysis of the amounts of metal bioaccumulated by whole organism and by the gills, estimates of nymph activity within the sediment, and results from earlier lab studies have generated several hypotheses on the involved mechanisms. We propose that ingested sediment is the predominant route of exposure and that the gut acts as a selective barrier that favors organic Hg absorption.

Relationships among developmental stage, metamorphic timing, and concentrations of elements in Bullfrogs (Rana catesbeiana)

“…Consumption of resources is determined by larval physiology and behavior, which also likely vary seasonally due to differences in temperature, dissolved oxygen, and predation pressure. For example, the ability of larvae to sequester or excrete elements may differ due to seasonal variation in environmental factors (e.g., temperature [39,40]) that affect larval physiology. Future studies that examine seasonal differences in bioavailability of trace elements and the effects of differences in food resources and physical environments on toxico-kinetics will be of value for predicting risk to overwintering individuals as well as to species that breed at different times of the year.…”

Total mercury and methylmercury in sediments and in the polychaeteNereis diversicolor at Groot Buitenschoor (Scheldt estuary, Belgium)

“…The highest sediment bioturbation due to N. diversicolor burrows were also found in spring and summer (Davey, 1993). Whether considered in isolation or in interaction with other abiotic factors, temperature has been shown to play an important role on Hg bioaccumulation by other benthic invertebrates such as nymphs of the burrowing mayfly Hexagenia rigida (Odin et al, 1994).…”

Influence of temperature on Cd accumulation by species of the biomonitor Chaoborus

“…Reports of temperature influencing metal bioaccumulation are generally not followed up with an identification of the biological processes responsible for the effect. Speculations to explain metal bioaccumulation-temperature interactions have included changes in the rates at which food is ingested (Odin et al 1994), water is passed over the gills (White and Rainbow 1984), metals cross biological membranes (Bervoets et al 1996), and metal binding proteins are produced (Douben 1989). However, there are no published experimental studies explaining how temperature influences trace metal accumulation by freshwater invertebrates.…”