Renato Baudo

Field validation of sediment zinc toxicity

A field study was conducted to validate concentrations of zinc in freshwater sediments that are tolerated by benthic macroinvertebrate communities and to determine whether a relationship exists with the acid volatile sulfide (AVS)-simultaneously extracted metal (SEM) model. In both the lake and riverine systems, one sediment type was high in AVS and one low in AVS, which resulted in zinc-spiked sediments that ranged from low to high SEM to AVS ratios. The colonization trays were sampled seasonally, ranging from 6 to 37 weeks of exposure, and were evaluated using several appropriate benthic indices. Results of the field evaluations at the four test sites confirmed the validity of the AVS-SEM model, predicting benthic macroinvertebrate effects correctly 92% of the time. In sediments where the SEM to AVS ratio or the AVS and organic (OC)-normalized fractions exceeded 8 and 583 micromol/g of OC, toxicity was observed from the zinc-spiked sediments. Conversely, when the SEM to AVS ratio or OC-normalized AVS fractions were less than 2 or 100 micromol/g of OC, no toxicity was observed. In the range of 148 to 154 micromol/g of OC, toxicity varied in two treatments. Total zinc concentrations in sediments showed no relationship to benthic effects. The most impaired benthic community occurred in the high-gradient stream sediments, which had low OC and AVS concentrations and SEM to AVS ratios of 33 and 44 in the spiked sediments. Five to six benthic metrics were depressed at SEM to AVS ratios of 8.32 and 9.73. The no-observed-effect level appeared to be near a SEM to AVS ratio of 2, with slight to no effects between ratios of 2.34 and 2.94. No sites with ratios of less than 2 showed any adverse effects.

Characterizing sediment acid volatile sulfide concentrations in European streams

Sediment acid volatile sulfide (AVS) concentrations were measured in wadeable streams of a wide variety of ecoregions of western Europe (84 sites in 10 countries and nine ecoregions) to better understand spatial distribution and ecoregion relationships. Acid volatile sulfide has been shown to be a major factor controlling the bioavailability and toxicity of many common trace metals, such as Cd, Cu, Ni, Pb, and Zn. Sediment characteristics varied widely. The ratio of the sum of the simultaneously extracted metals (SEM) to AVS ranged from 0.03 to 486.59. The sigmaSEM-AVS ranged from -40.02 to 17.71 micromol/g. On a regional scale, sediment characteristics such as dominant parent soil material showed significant trends in AVS distribution and variation by ecoregion. Total Fe and Mn were correlated weakly with SEM concentrations. Three AVS model approaches (i.e., the SEM:AVS ratio, SEM-AVS difference, and carbon normalization) were compared at threshold exceedance levels of SEM/AVS > 9, SEM-AVS > 2, and SEM-AVS/foc > 150 micromol/g organic carbon (OC). Only 4.76% of the sediments exceeded all three AVS thresholds; 22.6% of the sediments exceeded two models; and 13% of the sediments exceeded one model only. Using the SEM:AVS, SEM-AVS, and fraction of organic carbon models, and including site-specific data and regional soil characteristics, ecoregions 1 (Portugal), 3 (Italy), 4 (Switzerland), and 9 (Belgium/Germany) had the highest potential metals toxicity; ecoregions 13 and 8 (Belgium/France) showed the lowest potential toxicity. However, because AVS can vary widely spatially and temporally, these data should not be considered as representative of the sampled ecoregions. The general relationship between AVS levels and sediment characteristics provides some predictive capability for wadeable streams in the European ecoregions.

Phytotoxicity assessment of Lake Orta sediments

Abstract Seed germination and root elongation tests, as a common germination index, were used to evaluate contamination of liquid and solid phases of sediments of Lake Orta (Italy). Protocols for these tests were developed after a literature survey and an investigation of the proper conditions for the germination of commercially available seeds of Cucumis sativus (cucumber), Lactuca sativa (lettuce) and Lepidium sativum (watercress). The three plant species responded differently to three types of samples, overlying water, pore water and whole sediment. The most toxic responses occurred in tests on solid samples, where the germination indices were statistically significantly decreased. Results from tests on sediment, pore water and overlying water indicated that liming treatment has reduced pollutant loading and has improved conditions at the water-sediment interface. However, even though superficial layers of sediments were usually less toxic than those deposited in pre-liming periods, the germination ind...

In situ tests to assess the potential toxicity of aquatic sediments

This article reviews the methodological approaches currently used to assess the potential toxicity of aquatic sediments. In the past, the main use of in situ tests has been the field validation of results obtained by means of traditional methods (chemical analyses, inventory of the benthic communities, and laboratory toxicity testing). However, in situ techniques could also be used for a preliminary screening of sediment ecological risk assessment. At present, we suggest this approach for environments suspected to be contaminated, limiting the complex (and expensive) studies based on the traditional chemical analyses and laboratory toxicity testing to cases in which the necessity of a complete sediment risk assessment is already proved.

Pollution and recovery of Lake Orta (Italy): Resilience at work?

This paper attempts to fit the history of pollution and recovery of Lake Orta, Italy, to the ecological theory of resilience , or the ability to restore structure following perturbation. The evolution of this lake can be represented by a model of a folded surface. In the case of Lake Orta, a disturbance, represented by the onset of pollution in 1926, determined the transition to conditions of an extreme environment . If an opposite change is imposed on the environment (in this case, the liming of the whole lake), the model predicts that the ecosystem will not simply revert to the pathway that it has followed up to this point, but will evolve in a different way (hysteresis). Ultimately, the system could arrive either at similar (but never completely identical) conditions to those existing prior to the disturbance, or at some completely different state. The variations of phytoplankton, zooplankton, benthos, and fish in Lake Orta have been summarized by applying a stochastic exponential population growth model. This model succeeds in showing how resilience and resistance combine together, offering a fairly good description of both the pollution and the recovery of the lake. It can be concluded that at least nothing contradicts the hypothesis that past changes can be explained by the ecological theory of resilience and resistance.