Effects of complexing agents on the distribution of Hg(II) species provided by food to starfishLeptasterias polaris

Abstract

Mature starfish Leptasterias polaris were exposed to labelled mercury (II) species via food contaminated at a level of 5.0 J.Lg g-1 . The distribution of inorganic Hg and methylmercury (MeHg) in starfish organs and tissues and the effect of a series of complexing agents on mercury translocation between organs and tissues were examined over a 24-h period. The distribution of mercury species in coelomic fluid components, ammonia excretion rate and mercury excretion were also measured. The highest concentrations were observed in the stomach (the source organ) and in pyloric caecum (up to 0.32 J.Lg g-1 wet weight for inorganic Hg and 0.22 J.Lg g-1 for MeHg). Concentrations of MeHg in gonads ranged from~ 0.01 to 0.08 J.Lg g-1 whereas concentrations of inorganic Hg never exceeded 0.06 J.Lg g-1.1n all studied cases, mercury concentration was very low the coelomic fluid(~ 0.01 J.Lg g-1 ). The short-term distribution of Hg species via contaminated food in starfish L. polaris seems to be controlled by the haemal system, a primitive circulatory system responsible for the transport of soluble nutrients from the digestive track towards organs and tissues, but a possible role of the coelomic fluid can not be excluded. Very low Hg contents were observed in gonads and in the coelomic fluid which fills the general cavity. Except for mercaptoethanol (merOH) and dimercaptosuccinic acid (DMSA), the addition of complexing agents to the food had little effect on the distribution of Hg species. MerOH appeared as an efficient carrier for methylmercury transport through the digestive system. DMSA enhanced the translocation of inorganic mercury from stomach and pyloric caecum toward external tissues and markedly increased its excretion.

Distribution kinetics of trophic single doses of methylmercury, tributyltin, and corresponding inorganic ions in the starfish Leptasterias polaris

“…Both hypothesis about instantaneous and linear distribution were clearly confirmed by the constant distribution of metal in Compartment R, and by autoradiograms showing homogeneous labelling of pyloric caeca a few hours after contamination, indicating that chemicals entering the starfish via the stomach were distributed very rapidly and linearly within each studied compartment. The low and negligible excretion of mercury species by starfish within a 24 h exposure period was first observed in a study conducted by Maheu & Pelletier (1994) on excretion rates of inorganic 203Hg(II) and CH3203Hg(I~) taken from contaminated food. Less than 10% of ingested labelled mercury was found in surrounding seawater after 24 h. In the present series of experiments, no feces or particulate suspended matter were observed and the high labelling of the rectal caeca1 walls is indicative of the high absorption capacity of these organs; labelled compounds were thus retained within Compartment E. Values of r2 of fitted curves for both compartmental models and sums of squares of deviations between observed and predicted values provide a clear quantitative indication of the validity of the approach used to model experimental results.…”

Distribution kinetics of trophic single doses of methylmercury, tributyltin, and corresponding inorganic ions in the starfish Leptasterias polaris

“…Both hypothesis about instantaneous and linear distribution were clearly confirmed by the constant distribution of metal in Compartment R, and by autoradiograms showing homogeneous labelling of pyloric caeca a few hours after contamination, indicating that chemicals entering the starfish via the stomach were distributed very rapidly and linearly within each studied compartment. The low and negligible excretion of mercury species by starfish within a 24 h exposure period was first observed in a study conducted by Maheu & Pelletier (1994) on excretion rates of inorganic 203Hg(II) and CH3203Hg(I~) taken from contaminated food. Less than 10% of ingested labelled mercury was found in surrounding seawater after 24 h. In the present series of experiments, no feces or particulate suspended matter were observed and the high labelling of the rectal caeca1 walls is indicative of the high absorption capacity of these organs; labelled compounds were thus retained within Compartment E. Values of r2 of fitted curves for both compartmental models and sums of squares of deviations between observed and predicted values provide a clear quantitative indication of the validity of the approach used to model experimental results.…”

Exposure to methylmercury and inorganic mercury in the food does not lead to trophic magnification in the sea star Asterias rubens

“…A. rubens accumulates mercury from both water (Rouleau et al, 1993;Sorensen and Bjerregaard, 1991) and from food in short-term experimental investigations (Bjerregaard et al, 2018) and so does the starfish Leptasterias polaris (Maheu and Pelletier, 1994;Pelletier and Larocque, 1987;Rouleau et al, 1995a, b) in different experimental settings. It is not known if prolonged exposure to methylmercury and inorganic mercury in the food will lead to trophic magnification [here defined as increase in concentration from one step in the food chain to the next] of mercury in A. rubens.…”

Distribution kinetics of trophic single doses of methylmercury, tributyltin, and corresponding inorganic ions in the starfish Leptasterias polaris

“…Both hypothesis about instantaneous and linear distribution were clearly confirmed by the constant distribution of metal in Compartment R, and by autoradiograms showing homogeneous labelling of pyloric caeca a few hours after contamination, indicating that chemicals entering the starfish via the stomach were distributed very rapidly and linearly within each studied compartment. The low and negligible excretion of mercury species by starfish within a 24 h exposure period was first observed in a study conducted by Maheu & Pelletier (1994) on excretion rates of inorganic 203Hg(II) and CH3203Hg(I~) taken from contaminated food. Less than 10% of ingested labelled mercury was found in surrounding seawater after 24 h. In the present series of experiments, no feces or particulate suspended matter were observed and the high labelling of the rectal caeca1 walls is indicative of the high absorption capacity of these organs; labelled compounds were thus retained within Compartment E. Values of r2 of fitted curves for both compartmental models and sums of squares of deviations between observed and predicted values provide a clear quantitative indication of the validity of the approach used to model experimental results.…”

Exposure to methylmercury and inorganic mercury in the food does not lead to trophic magnification in the sea star Asterias rubens

“…A. rubens accumulates mercury from both water (Rouleau et al, 1993;Sorensen and Bjerregaard, 1991) and from food in short-term experimental investigations (Bjerregaard et al, 2018) and so does the starfish Leptasterias polaris (Maheu and Pelletier, 1994;Pelletier and Larocque, 1987;Rouleau et al, 1995a, b) in different experimental settings. It is not known if prolonged exposure to methylmercury and inorganic mercury in the food will lead to trophic magnification [here defined as increase in concentration from one step in the food chain to the next] of mercury in A. rubens.…”

Distribution kinetics of trophic single doses of methylmercury, tributyltin, and corresponding inorganic ions in the starfish Leptasterias polaris

“…Both hypothesis about instantaneous and linear distribution were clearly confirmed by the constant distribution of metal in Compartment R, and by autoradiograms showing homogeneous labelling of pyloric caeca a few hours after contamination, indicating that chemicals entering the starfish via the stomach were distributed very rapidly and linearly within each studied compartment. The low and negligible excretion of mercury species by starfish within a 24 h exposure period was first observed in a study conducted by Maheu & Pelletier (1994) on excretion rates of inorganic 203Hg(II) and CH3203Hg(I~) taken from contaminated food. Less than 10% of ingested labelled mercury was found in surrounding seawater after 24 h. In the present series of experiments, no feces or particulate suspended matter were observed and the high labelling of the rectal caeca1 walls is indicative of the high absorption capacity of these organs; labelled compounds were thus retained within Compartment E. Values of r2 of fitted curves for both compartmental models and sums of squares of deviations between observed and predicted values provide a clear quantitative indication of the validity of the approach used to model experimental results.…”

Exposure to methylmercury and inorganic mercury in the food does not lead to trophic magnification in the sea star Asterias rubens

“…A. rubens accumulates mercury from both water (Rouleau et al, 1993;Sorensen and Bjerregaard, 1991) and from food in short-term experimental investigations (Bjerregaard et al, 2018) and so does the starfish Leptasterias polaris (Maheu and Pelletier, 1994;Pelletier and Larocque, 1987;Rouleau et al, 1995a, b) in different experimental settings. It is not known if prolonged exposure to methylmercury and inorganic mercury in the food will lead to trophic magnification [here defined as increase in concentration from one step in the food chain to the next] of mercury in A. rubens.…”