Penguin guano trace metals release to Antarctic waters: A kinetic modelling.

Penguin guano has been considered as a suitable bioindicator of the exposure to environmental contaminants in Antarctic environment. Although trace metal content values in penguin guano have been widely reported, the kinetics of their mobility in seawater have not been determined. In the present study, we have estimated the release rate of dissolved Cd, Co, Cu, Fe, Mn, Mo, Ni, Pb, V, and Zn from Gentoo (Pygoscelis papua) penguins guano to Antarctic seawater by 120 h laboratory and at external natural conditions of temperature and light experiments. A mathematical model using two metal pools guano (labile and equilibrium) and seawater compartments considering pseudo-first-order kinetics, is proposed in order to interpret and predict the release of trace metals. A good statistical agreement between experimental and modelled concentration values allows us obtention of kinetic parameters and partition coefficients (Kdi). These values allow to estimate releases into seawater from 5400 to 6.3 µg/day·penguin of Cu and V, respectively. More than 50 % of the initial content of all the studied elements are released during the first two hours, reaching 90 % release in the decreasing order of speed Ni â‰« Cu ≈ Mo > Mn > Co > Cd ≈ Pb; periods of up to one hour, Fe, V and Zn reach a maximum release and are then readsorbed. Equilibrium releases >90 % for Mo and Cd, and 55 % - 46 % for Co, Ni, Pb and Mn are obtained; Zn with 5.4 %, V with 1.7 % and Fe with 0.88 % show the lowest values. With an overwhelming growth of estimated population south of 60°S of 259.750 breeding pairs we estimate that the Gentoo penguin population is releasing annually in the Southern Ocean, 716 kg Cu, 188 kg Mn, 113 kg Fe, 102 kg Zn, 17.7 kg Mo, 12.0 kg Ni, 8.70 kg Cd, 4.59 kg Co, 6.27 kg Pb and 0.790 kg V of soluble metals.

Modelling the bioconcentration of Zn from commercial sunscreens in the marine bivalve Ruditapes philippinarum.

Sunscreens contain ZnO particles used as a UV filter cause adverse effects in the marine environment through the release of this metal into seawater and its bioaccumulation in organisms. A mathematical model using sunscreen colloidal residues, seawater and R. philippinarum clams as differentiated compartments, is proposed in order to interpret both the kinetic pattern and the bioaccumulation of Zn in clams. Two kinetic laboratory experiments were conducted, both with and without clams exposed to sunscreen concentrations from 0 to 200 mg L-1. Both the lowest value of uptake rate coefficient obtained when 5 mg L-1 of sunscreen is added (0.00688 L g-1 d-1) and the highest obtained at sunscreen addition of 100 mg L-1 (0.0670 L g-1 d-1), predict a lower bioavailability of Zn in a complex medium such as the seawater-sunscreen mixtures, in comparison to those studied in the literature. The efflux rate coefficient from clams to seawater increased from 0 to 0.162 d-1 with the sunscreen concentrations. The estimated value of the inlet rate coefficient at all studied concentrations indicates that there is a negligible colloidal Zn uptake rate by clams, probably due to the great stability of the organic colloidal residue. An equilibrium shift to higher values of Zn in water is predicted due to the bioconcentration of Zn in clams. The kinetic model proposed with no constant Zn (aq) concentrations may contribute to a more realistic prediction of the bioaccumulation of Zn from sunscreens in clams.