title: Variability of microcystin cell quota in metapopulations of Planktothrix rubescens: causes and implications for water management.
abstract: In this study, we investigated the relationships between microcystin (MCs) concentrations and the biovolumes of Planktothrix rubescens (BPr) in 2 natural lakes (Pusiano and Garda) and 2 artificially dammed reservoirs (Occhito and Ledro) in Italy. In all the considered water bodies, P. rubescens was the dominant cyanobacterium. All the lakes were characterized by significant relationships between MCs and BPr, with limited variability in the MC quota (the content of MCs per unit of biovolume) within each water body compared with the variability between sites. The results were consistent with the development of specific MC-genotypes, with moderate seasonal and spatial changes in the proportion between toxic and non-toxic strains. The MC cell quota obtained in our work (ECQ, Environmental Cell Quota) were in the same range of values computed on the basis of analyses made on environmental samples dominated by P. rubescens or Planktothrix agardhii, and on isolates of the same two species (<1 to over 10 μg mm(-3)). Besides the usual ordinary least square regressions, models have been evaluated by using quantile regression, a method that allows estimating the conditional median or other quantiles of the response variable. We showed that the use of quantile regressions has different advantages, which included the computation of MC quota based on the whole range of available data, the robustness against outliers, and the ability to estimate models also in cases where there is no or only weak relationships. The highest ECQ values estimated from 95% quantile regressions in specific water bodies might be used to estimate the worst-case MC concentrations from algal abundances. Nevertheless, it was stressed that a realistic assessment of toxicity and potential adverse health effects necessarily should take into account the toxicity potential of the more abundant MC-congeners produced by specific cyanobacteria populations.
authors.affiliation: IASMA Research and Innovation Centre, Istituto Agrario di S. Michele all'Adige - Fondazione E. Mach, Via E. Mach 1, 38010 S. Michele all'Adige, Trento, Italy. Electronic address: nico.salmaso@fmach.it.
authors.forename: Nico
authors.initials: N
authors.lastname: Salmaso
authors.affiliation: National Research Council of Italy, Water Research Institute, UOS Brugherio, Via del Mulino, 19, 20861 Brugherio, MB, Italy.
authors.forename: Diego
authors.initials: D
authors.lastname: Copetti
authors.affiliation: IASMA Research and Innovation Centre, Istituto Agrario di S. Michele all'Adige - Fondazione E. Mach, Via E. Mach 1, 38010 S. Michele all'Adige, Trento, Italy.
authors.forename: Leonardo
authors.initials: L
authors.lastname: Cerasino
authors.affiliation: IASMA Research and Innovation Centre, Istituto Agrario di S. Michele all'Adige - Fondazione E. Mach, Via E. Mach 1, 38010 S. Michele all'Adige, Trento, Italy; Human and Environmental Toxicology Group, Department of Biology, University of Konstanz, P.O. Box X-918, D-78457 Konstanz, Germany.
authors.forename: Shiva
authors.initials: S
authors.lastname: Shams
authors.affiliation: IASMA Research and Innovation Centre, Istituto Agrario di S. Michele all'Adige - Fondazione E. Mach, Via E. Mach 1, 38010 S. Michele all'Adige, Trento, Italy; Department of Biology, University of Florence, Via La Pira, 4, Florence, Italy.
authors.forename: Camilla
authors.initials: C
authors.lastname: Capelli
authors.affiliation: IASMA Research and Innovation Centre, Istituto Agrario di S. Michele all'Adige - Fondazione E. Mach, Via E. Mach 1, 38010 S. Michele all'Adige, Trento, Italy.
authors.forename: Adriano
authors.initials: A
authors.lastname: Boscaini
authors.affiliation: National Research Council of Italy, Water Research Institute, UOS Brugherio, Via del Mulino, 19, 20861 Brugherio, MB, Italy.
authors.forename: Lucia
authors.initials: L
authors.lastname: Valsecchi
authors.affiliation: National Research Council of Italy, Water Research Institute, UOS Brugherio, Via del Mulino, 19, 20861 Brugherio, MB, Italy.
authors.forename: Fiorenzo
authors.initials: F
authors.lastname: Pozzoni
authors.affiliation: National Research Council of Italy, Water Research Institute, UOS Brugherio, Via del Mulino, 19, 20861 Brugherio, MB, Italy.
authors.forename: Licia
authors.initials: L
authors.lastname: Guzzella
mesh_terms: D000458:Cyanobacteria / Q000737:chemistry / Q000302:isolation & purification*; D005618:Fresh Water; D052998:Microcystins / Q000032:analysis*; D014871:Water Microbiology; D018508:Water Purification / Q000379:methods*
chemical_list: D052998:Microcystins
keywords: Cell quota; Cyanobacteria; Microcystins; Planktothrix; Quantile regressions; Risk assessment