Environmental Pollution of the Pearl River Estuary, China by Wen-Xiong Wang & Philip S. Rainbow

Author:Wen-Xiong Wang & Philip S. Rainbow
Language: eng
Format: epub
ISBN: 9783662618349
Publisher: Springer Berlin Heidelberg

Accumulation

There is great variation in the accumulated trace metal concentrations of invertebrates, between even relatively closely related species for one metal, and within one species for different metals, even in the absence of raised metal bioavailabilities.

This interspecific variation is well exemplified by the different accumulation patterns of the trace metal zinc within the single taxon, the crustaceans.

Barnacles are strong accumulators of zinc with little, if any, significant excretion of zinc taken up from solution and the diet, resulting in very high body concentrations of stored zinc (Luoma and Rainbow 2008; Rainbow 2018). Such accumulated body concentrations often reach in excess of 10,000 μg g−1 dry weight and rise with increased total local bioavailability of zinc to the barnacle (Rainbow 2018). This accumulated zinc is necessarily stored in a form that has been detoxified and is not metabolically available to cause any ecotoxic effects on the barnacle’s physiology, in this case as zinc pyrophosphate granules (Rainbow and Luoma 2011a, Rainbow 2018).

On the other hand, caridean decapod crustaceans such as the intertidal palaemonid Palaemon elegans regulate the body concentration of zinc to about 80 μg g−1 over a wide range of zinc bioavailabilities (and hence uptake rates) (Rainbow and Luoma 2011a; Rainbow 2018). The decapod maintains this approximately constant body concentration by balancing increased excretion with the increased uptake rate of zinc, until, beyond a threshold dissolved bioavailability, the body zinc concentration accumulated over the period of exposure increases progressively with the zinc exposure concentration until death (Rainbow and White 1989). At this point of regulation breakdown, P. elegans can no longer match the rate of zinc excretion to the very high rate of zinc uptake and net accumulation of body zinc begins. The difference between the rates of zinc uptake and excretion is now such that a threshold concentration of metabolically available zinc in the body is exceeded, and toxicity follows (Rainbow and Luoma 2011a).

The zinc accumulation pattern of amphipod crustaceans is also that of net accumulation with detoxified storage (Rainbow 2018). The net accumulation in these crustaceans is, however, much weaker than that of the barnacles because of the presence of zinc excretion (Rainbow and Luoma 2011a; Rainbow 2018). In amphipod crustaceans, accumulated zinc is stored temporarily in detoxified metal-rich granules in the ventral caeca of the alimentary tract to be excreted with the faeces on completion of the cell cycle of the ventral caeca epithelial cells (Rainbow and Luoma 2011a; Rainbow 2018). This is not a process of regulation, for the body concentration of zinc in the amphipods reaches a new steady-state level as zinc bioavailabilities change. The zinc bioavailability is reflected in the changing number of zinc-rich granules in the ventral caeca at any one time, and hence the zinc concentration of both the ventral caeca and the whole body to which the ventral caeca make a major contribution. The body concentration of zinc in an amphipod from an uncontaminated habitat is of the order of 50–80 μg g−1 (Rainbow and Luoma 2011a; Rainbow 2018). In zinc-contaminated habitats,

Download

Copyright Disclaimer:
This site does not store any files on its server. We only index and link to content provided by other sites. Please contact the content providers to delete copyright contents if any and email us, we'll remove relevant links or contents immediately.