Ecotoxicological Risk Assessment of Metal and Hydrocarbon Pollution in Eutrophic Sediments from Urban Tropical Lagoons

Urban tropical lagoons are often impacted by eutrophication, silting processes, metal and polycyclic aromatic hydrocarbons (PAH) contamination, compromising important ecosystem services. However, the toxicity of their bottom sediments is still poorly investigated in South America. Aiming to contribute to filling this gap, results related to sediment quality assessments conducted in different lagoon systems from Rio de Janeiro city (Brazil) will be presented. Those studies involved the use of different lines of evidence, including sediment characterization, determination of metals and hydrocarbon (PAHs), acute toxicity tests with burrowing amphipods (Tiburonella viscana) and chronic tests with sea-urchin (Echinometra lucunter). The results consist of the determination of key contaminants and critical zones of contamination that should be a priority for restoration actions.

Land Disposal of Metal-contaminated Dredged Sediments and Ecotoxicological Risks to Soil Biota

Estuarine and fluvial systems from South America countries have been impacted with domestic wastes and industrial activities due to the expansion of urbanized areas. Most of these environments are silted, eutrophic and highly contaminated with toxic metals and domestic sewage. Due to this reality, the dredging of bottom sediments has become a common practice to minimize ecological damages and preserve ecosystem services. The disposal of dredged sediment in soils is usual, and the use of these materials as soil amendments in the agriculture, beach nourishments and expansion of wetlands is also frequent. However, the presence of contaminants in these materials can cause adverse effects on soil biota and should be carefully monitored by using bioassays with ecologically representative soil organisms (e.g., earthworms and collembolans). Results related to ecotoxicological assessments of dredged sediments from different estuaries of the Rio de Janeiro State will be presented, taking into consideration scenarios of dredged sediment disposal in distinct tropical soils classes.

Dr. Ricardo Cesar is a geographer/geochemist and a Professor at the Federal University of Rio de Janeiro (UFRJ) - Geosciences Institute, Department of Geography. His career is strongly based on a multi-disciplinary background (including chemistry, geochemistry, physical geography, geology, ecology, toxicology and engineering) which led him to a holistic perspective on environmental issues, especially those ones involving toxics metals and domestic sewage pollution. The pollution of soils, rivers and estuaries induced by mining tailing deposition has also been an important focus of his research themes. In 2015, Ricardo Cesar founded the Soil Ecology and Ecotoxicological Laboratory (LECOTOX) at the UFRJ, whose focus is to understand the spatial variability of contaminants and their bioavailability levels in soil and aquatic ecosystems, including the mapping ecological and human health risks (http://www.geografia.ufrj.br/laboratorio-ecologia-ecotoxicologia-solos/).

Adressing Complexity and Feedbacks in Ecological Risk Assessment for Rehabilitation of a Mine Site Near a World Heritage Site

Ecological Risk Assessments (ERAs) are important tools for supporting evidence-based decision making. However, most ERA frameworks rarely consider complex ecological feedbacks, which limits their capacity to evaluate risks at community and ecosystem levels of organisation. Method: We used qualitative mathematical modelling to add additional perspectives to previously conducted ERAs for the rehabilitation of the Ranger Uranium mine (Northern Territory, Australia) and support an assessment of the cumulative risks from the mine site. Using expert elicitation workshops, separate qualitative models and scenarios were developed for aquatic and terrestrial systems. The models developed in the workshops were used to construct Bayes Nets that predicted whole-of-ecosystem outcomes after components were perturbed. Results: The terrestrial model considered the effect of fire and weeds on established native vegetation that will be important for the successful rehabilitation of Ranger. It predicted that a combined intervention that suppresses both weeds and fire intensity gave similar response predictions as for weed control alone, except for lower levels of certainty to tall grasses and fire intensity in models with immature trees or tall grasses. However, this had ambiguous predictions for short grasses and forbs, and tall grasses in models representing mature vegetation. The aquatic model considered the effects of magnesium (Mg), a key solute in current and predicted mine runoff and groundwater egress, which is known to adversely affect many aquatic species. The aquatic models provided support that attached algae and phytoplankton assemblages are the key trophic base for food webs. It predicted that shifts in phytoplankton abundance arising from increase in magnesium to receiving waters, may result in cascading effects through the food-chain. Conclusion: The qualitative modelling approach was flexible and capable of modelling both gradual (i.e. decadal) processes in the mine-site restoration and the comparatively more rapid (seasonal) processes of the aquatic ecosystem. The modelling also provides a useful decision tool for identifying important ecosystem sub-systems for further research efforts.

Jeffrey Dambacher's background was originally in the ecology of stream fishes. A desire to understand the complex relationships of fish communities, rivers and watersheds led him to the method of qualitative mathematics as a tool to address complex systems. With CSIRO this work has been expanded to address problems of integrated monitoring and management of socio-ecological systems such as the Great Barrier Reef, marine ecosystems of Australia’s exclusive economic zone, Mediterranean fisheries and aquaculture systems in Tasmania, Chile and France.

Ecotoxicology: how to answer when they say "So what?"

Ecological risk assessment for environmental pollutants should be a probabilistic forecast of the effects of contaminants at the level of biological populations. Effects at the level of individuals, except for impacts on humans and endangered species, are often considered less important for environmental management. Although still in wide use, deterministic models cannot adequately portray the environmental stochasticity that is ubiquitous in nature. The probabilistic analysis should not be reduced to a simplistic summary based on the mean. A comprehensive assessment requires consideration of the full distribution of risks. There are two ways to visualize a distributional risk assessment of a chemical’s impact on a population. The first is to display, side by side, the two risk distributions arising from separate simulations with and without the impact but alike in every other respect. Alternatively, one can display a probability distribution of the differences between population trajectories with and without impact but alike in every other respect. Like all scientific forecasts, an ecological risk assessment requires appropriate uncertainty propagation. This can be accomplished by using a mixture of interval bounding analysis and Monte Carlo simulation techniques.

Scott Ferson is the director of the Institute for Risk and Uncertainty. Previously, he was senior scientist at the research firm Applied Biomathematics. He holds a Ph.D. in ecology and evolution from Stony Brook University in New York. His research in population-level ecology focuses on developing quantitative assessment strategies with poor data and limited structural knowledge about the system.