S.TR.E.A.M., system for trace element assessment with mosses. An equation to estimate mercury concentration in freshwaters

Hundred experiments of Hg bioaccumulation with the aquatic moss Rhynchostegium riparioides (Hedw.) C.E.O. Jensen transplanted under laboratory conditions were carried out with the aim of (1) measuring the metal uptake at increasing water concentrations (0.25–128 μg Hg2+ L−1) and increasing exposure time (24–189 h), (2) studying the influence of pH (6.3–8.5) and water concentration of Na (3–114 mg L−1), Ca (62–125 mg L−1) and Mg (13–54 mg L−1) on the metal uptake, (3) achieving a database for mathematical and statistical elaborations, and, (4) producing an equation modelling the uptake. A linear uptake was observed for water concentrations <=4 μg Hg2+ L−1, while a saturation curve was observed at higher concentrations. Uptake followed a 3-stage trend for increasing exposure times: a phase of rapid accumulation (4–5 d), followed by an equilibrium plateau (2–3 d) and then by a second accumulation phase. The factor influence study revealed that variations in pH or water concentration of alkaline metals, within the range of typical values in freshwaters of NE Italy, did not produce significant differences (p > 0.05) in the Hg uptake ratio (0.496 × 105 <= Bio Accumulation Factor <= 1.73 × 105). From a database of 28 Hg concentrations in mosses exposed to 0.25–4 μg Hg2+ L−1 for 24–114 h, a mathematical equation was produced, to assess Hg micro-contamination in water. The difference between predicted and real concentration was generally included in the range ± 50%.