ABSTRACT-The decapod crustaceans Palaernon elegans Rathke and Palaernonetes varians (Leach) regulate their body concentrations of zinc to an approximately constant level (ca 76 to 82 and 90 to 99 11g Zng-' dry wt respectively) when exposed to a wide range of dissolved Zn concentrations, until a threshold dissolved concentration when regulation breaks down and net accumulation of body Zn begins. This threshold concentration decreases with decrease in salinity, from 100 "/u SW to 50 O/ O SW in the case of P. elegans (ca 92 to 27 pg Zn 1-' respectively) and from 100 % SW to 5% SW in the case of P. varians (ca 191 to 19 pg Zn 1-' respectively), in correlation with increased rates of Zn uptake. P. elegans showed a further increased uptake rate in 25 SW (1.054 _t 0.385 yg Zn g-' d-l in 25 ' 1 0 SW vs 0.735 f 0.077 1-19 Zn g-' d-' in 100 % SW at 10°C in 56.2 pg Zn I-'), but had an atypical pattern of Zn regulation in raised Zn concentrations, probably as a result of atypically high Zn efflux caused by changes in water balance under osmotic stress. P. varians has a lower rate of Zn uptake than P elegans under identical physico-chemical conditions (1.80 2 0.61 vs 5-27 2 3.67 11g Zn g -' d-' in 100 [[g Zn 1-' in 5 0 % SW). Fifteen day acclimation of P. varians to either 50 or 25 % SW did not significantly change the subsequent mean rate of Zn uptake from 100 pg Zn 1-' in 2 5 % SW The body Zn concentration of P. varians transferred to dilute media of 25 and 5 O/O SW increased initially as a low salinity response but decreased again after 2 to 10 d to be regulated at ca 95pg Zn g-l It is concluded that Zn uptake and regulation in decapods are affected both by extrinsic physico-chemical factors and by intrinsic adaptations of the species concerned.

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The use of silver nanoparticles (AgNPs) is growing exponentially, especially in consumer products due to their excellent antimicrobial properties. However, concerns are growing on their possible negative effects on environmental and human health. AgNPs from consumer products enter aquatic ecosystems where their physicochemical properties including surface functionalization are critical to their impact on aquatic organisms. The effects of AgNPs coated with three different ligands; tyrosine (T-AgNP), epigallocatechin gallate (E-AgNP) and curcumin (C-AgNP) and Ag + ions on the freshwater green alga Raphidocelis subcapitata were investigated. Stability tests of AgNPs revealed that the coating significantly affects the fate and behaviour of AgNPs. All types of AgNPs tested and ionic silver were found to be toxic to the alga and differential growth inhibition of algae were observed from differently coated AgNPs, with the 48 h EC 50 of C-AgNPs, T-AgNPs and E-AgNPs being 0.155, 0.163 and 0.243 mg L −1 , respectively, in comparison with 0.051 mg L −1 for Ag + ions. Associated Ag in the algae increased with increased concentrations of all AgNPs and Ag + ions and the toxicity positively correlated to the associated Ag content in algae. The antioxidant enzymes glutathione S-transferase and catalase were activated in algal cells by the AgNPs and Ag + ions, but a consistent difference in response was not identified with different concentrations of NPs. This study shows the effects of the surrounding environment and surface functionalization of AgNPs on algae highlighting the importance of considering them in environmental risk assessment of AgNPs.