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Assimilation Efficiencies and Elimination Rates of Trace Metals Accumulated Through Trophic Pathway in the Freshwater Amphipod Gammarus fossarum


Core Concepts
The assimilation efficiencies (AE) and elimination rates of silver (Ag), cadmium (Cd), and zinc (Zn) in the freshwater amphipod Gammarus fossarum were determined using a pulse-chase-feeding method with two contrasting food sources: alder leaves and chironomid larvae.
Abstract
This study aimed to estimate the assimilation efficiencies (AE) and elimination rates of Ag, Cd, and Zn in the freshwater amphipod Gammarus fossarum when exposed to contaminated alder leaves or chironomid larvae. The key findings are: Regardless of the metal, gammarids eliminated the highest proportions of ingested trace elements during the first 48 hours after exposure, with similar elimination rates (kes) among metals (0.14-0.18 h-1). The second kinetic phase showed lower elimination rates (kel), with Tbl1/2 of 120 ± 35 h, 124 ± 25 h, and infinity for Zn, Cd, and Ag, respectively. This suggests that Ag is strongly retained in internal tissues of gammarids. The AE values were ranked as Cd (39 ± 3%) > Zn (15 ± 2%) > Ag (5.2 ± 1.1%) for alder leaves. For Cd and Zn, the AE were higher when gammarids were fed with leaves than with larvae (19 ± 2% and 9.1 ± 1.2%, respectively), suggesting the food matrix influences metal bioavailability and assimilation. The differences in AE and elimination rates between food types indicate that the subcellular distribution and bioaccessibility of metals in the food source are important factors controlling trophic transfer in gammarids.
Stats
The assimilation efficiency (AE) of Cd was 39 ± 3% in alder leaves and 19 ± 2% in chironomid larvae. The AE of Zn was 15 ± 2% in alder leaves and 9.1 ± 1.2% in chironomid larvae. The AE of Ag was 5.2 ± 1.1% in alder leaves. The biological half-life (Tbl1/2) of Cd and Zn was 124 ± 25 h and 120 ± 35 h, respectively, when gammarids were fed with alder leaves. The biological half-life (Tbl1/2) of Ag was infinite when gammarids were fed with alder leaves.
Quotes
"Cd has the highest assimilation efficiency (39% for leaves and 19% for larvae), followed by Zn (15% for leaves and 9% for larvae) and Ag (5% for leaves)." "for Cd and Zn, the AE were higher when gammarids were fed with leaves than with larvae." "the elimination rates of metals seem to depend more on the food matrix than on the metal assimilated."

Deeper Inquiries

How do the subcellular partitioning and bioaccessibility of metals in different food sources (e.g., plant vs. animal) influence their trophic transfer and bioaccumulation in gammarids?

In the context of the study on metal bioaccumulation in Gammarus fossarum, the subcellular partitioning and bioaccessibility of metals in different food sources play a crucial role in influencing their trophic transfer and bioaccumulation in gammarids. When considering plant sources, such as alder leaves, the metals are likely to be adsorbed on the inert matrix of the leaves. This passive adsorption allows for the metals to be easily desorbed in a free form or weak ionic complex once ingested by the gammarids. As a result, these metals become more bioavailable and are assimilated more rapidly by the gammarids. On the other hand, when the gammarids feed on animal sources like chironomid larvae, the metals are actively ingested by the live larvae, distributed among tissues, incorporated into cells, and taken up by detoxification mechanisms. This leads to the metals being strongly bound to various subcellular components within the larvae, making them less bioavailable and more slowly assimilated by the gammarids. The differences in subcellular partitioning and bioaccessibility between plant and animal food sources ultimately impact the trophic transfer of metals in gammarids. The higher assimilation efficiencies observed for metals from plant sources compared to animal sources suggest that the type of food ingested significantly influences the bioaccumulation of metals in gammarids. Understanding these mechanisms is essential for predicting how metals move through food webs and accumulate in aquatic organisms like gammarids.

What are the potential implications of the observed differences in metal assimilation and elimination between food types for the use of gammarids as bioindicators of metal contamination in aquatic ecosystems?

The observed differences in metal assimilation and elimination between different food types have significant implications for the use of gammarids as bioindicators of metal contamination in aquatic ecosystems. Accuracy of Metal Contamination Assessment: Understanding how different food sources affect metal assimilation and elimination in gammarids allows for a more accurate assessment of metal contamination levels in aquatic ecosystems. By considering the type of food ingested by gammarids, researchers can better interpret the recorded metal concentrations in these organisms. Validity of Biomonitoring Data: The variations in metal assimilation efficiencies between plant and animal sources highlight the importance of considering dietary pathways in biomonitoring studies using gammarids. Failure to account for these differences could lead to misinterpretation of bioaccumulation data and inaccurate assessments of metal pollution levels. Modeling and Predicting Metal Fate: The data on metal assimilation and elimination can be used to improve toxicokinetic models that predict the fate of metals in gammarids and other aquatic organisms. By incorporating information on food sources and their influence on metal bioaccumulation, more accurate models can be developed to understand metal dynamics in aquatic ecosystems. Long-Term Monitoring Strategies: The differences in metal retention observed, especially for silver, suggest that gammarids may serve as long-term indicators of metal contamination in environments. The strong retention of certain metals, like silver, could have implications for the fitness and population dynamics of gammarids over time, making them valuable indicators for monitoring metal pollution in aquatic ecosystems. Overall, the observed differences in metal assimilation and elimination between food types underscore the importance of considering dietary pathways when using gammarids as bioindicators of metal contamination. By taking these factors into account, researchers can enhance the accuracy and reliability of biomonitoring data in aquatic ecosystems.

Could the strong retention of silver in gammarids have any long-term consequences for the fitness and population dynamics of this species in contaminated environments?

The strong retention of silver in gammarids, as observed in the study, could have potential long-term consequences for the fitness and population dynamics of this species in contaminated environments. Toxicological Effects: Silver is known to have toxic effects on aquatic organisms, and the prolonged retention of silver in gammarids could lead to adverse health effects. Accumulation of silver in tissues over time may disrupt physiological processes, leading to reduced fitness, impaired reproduction, and increased mortality rates in gammarid populations. Bioaccumulation in Food Chains: The bioaccumulation of silver in gammarids can also have cascading effects on the food chain. As gammarids are an important part of aquatic ecosystems, their contamination with silver can result in the transfer of this metal to predators higher up in the food chain. This bioaccumulation can magnify the impact of silver contamination on ecosystem health. Population Dynamics: The long-term retention of silver in gammarids may alter their population dynamics in contaminated environments. Reduced reproductive success, increased susceptibility to diseases, and changes in behavior due to silver exposure can affect the overall population size and structure of gammarids in these environments. Ecosystem Impacts: Changes in gammarid populations can have broader ecosystem impacts. Gammarids play a key role in nutrient cycling, energy transfer, and food web dynamics in aquatic ecosystems. Any disruptions in gammarid populations due to silver contamination can have ripple effects on the entire ecosystem. In conclusion, the strong retention of silver in gammarids could have significant implications for their fitness and population dynamics in contaminated environments. It is essential to further investigate the long-term effects of silver contamination on gammarids and their role in aquatic ecosystems to better understand and mitigate the potential consequences of metal pollution on these organisms.
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