Transient Alterations in Streamwater Quality Induced by Pollution Incidents: Interim Losses Calculations and Compensation Alternatives Based on Habitat Equivalency Analysis.

Pollution incidents cause transient water quality alterations during the passage of contaminants' plume along watercourses, with plume passage period and contaminants' concentrations modelled by advection-dispersion equations. Despite being transient, water quality alterations can impose many impacts on the streamwater ecosystem services. This study proposes two frameworks based on Habitat Equivalency Analysis to be applied during assessments of streamwaters' pollution incidents and respective compensation panoramas: (1) Streamwater interim loss framework, to calculate interim loss debits caused by transient alterations in the streamwater quality; (2) Total credit framework, to calculate streamwater credits generated by improvements in selected watercourse's streamwater quality, produced by wastewater treatment plants in this study. The amount of credits calculated in the selected watercourses assists in the proposal of suitable compensatory remediation projects to offset interim losses. Frameworks' calculations are founded on IVA, a water quality index for protection of aquatic life and aquatic communities. Frameworks' calculations depend on three parameters: IVA, watercourses fluxes and the present value multiplier. The frameworks were calculated in ΔIVAxL, unit defined by multiplying sensed alterations in streamwater quality (as ΔIVA) and streamwater flux, in liters (L). The frameworks were applied to two major streamwater pollution incidents in Brazil, caused by the dam collapses of Mariana and Brumadinho, suggesting suitable compensatory remediations' projects for the respective streamwater interim losses. Depending on the selected project, Brumadinho compensation period varied from 2 to 5 years, with estimated costs in the 2020 Int.$ 5.7-18.7M range; Mariana compensation period varied from 8 to 20 years, with estimated costs in the 2020 Int.$ 16.7-58.1M range. Based on Brumadinho compensatory remediation projects, an average water pollution environmental damage value per interim loss was calculated, 1.17E-4 2020 Int.$/ΔIVAxL, which might be useful in comparing streamwater pollution evaluations around the world.

Monitoramento ecotoxicológico contínuo da qualidade de águas superficiais: equipamentos disponíveis / Continuous ecotoxicological monitoring of surface water quality: avaliable systems

Existem, atualmente, equipamentos de funcionamento automático e contínuo para a avaliação da toxicidade da água os quais utilizam organismos vivos como elementos sensores dos efeitos das substâncias químicas na água. Dentre eles, podem ser citados o "Teste Dinâmico com Daphnia", o "Stiptox", o "MusselMonitor®", o "Gymnotox®", o "Bio-Sensor®" e o "bbe Daphnia Toximeter", ou toxímetro. São observados os efeitos sobre o comportamento dos organismos sensores. Os critérios utilizados para avaliação do comportamento são o padrão de natação, a partir de vários componentes, ou padrão de abertura e fechamento de valvas ou, ainda, o de respiração ou consumo de oxigênio, dependendo do organismo utilizado. Estudos mostram que este tipo de avaliação pode ser mais sensível que o teste convencional que avalia letalidade, incluindo aqui concentração e velocidade de detecção do efeito. Esta abordagem permite que o gerenciador local da qualidade de recursos hídricos possa tomar uma decisão que envolva seus usos antes que um acidente ambiental tome proporções grandiosas ou antes mesmo que um acidente ocorra. Foram realizados ensaios com a substância de referência KCI. Os testes com o toxímetro tiveram duração de cerca de 30 horas, sendo que as primeiras 24 horas de exposição em água limpa (água de diluição); depois deste período, os organismos foram expostos à substância por 2 horas, no máximo, seguida de nova exposição à água de diluição por mais algumas horas, de modo a se avaliar a duração do efeito e a sua possível reversão a um nível normal. O resultados mostraram que, nas condições dos ensaios realizados, o efeito acusado pela exposição ao KCI foi reversível e a concentração que causa efeito foi similar à CL50;48h para Daphnia similis. Tal resultado indica que é possível se obter em menor tempo o resultado proveniente de testes convencionais e que a sensibilidade do ensaio não aumenta, já que a concentração detectada foi da mesma ordem de magnitude. Espera-se, com esse trabalho, contribuir para a gestão dos recursos hídricos ao se fazer uma avaliação de tais ferramentas promissoras para avaliar continuamente, e com rápido tempo de resposta, a qualidade da água para fins de proteção das comunidades aquáticas, conforme previsto pela Resolução CONAMA 20/86.

Nowadays, there are automatic and continuous systems which use living organisms as sensors of the toxic effects of chemicals dissolved in the water. Among them are the "Dynamic DaphniaTest", the "Stiptox", the "MusselMonitor®", the "Gymnotox®", the "Bio-Sensor®" and the "bbe Daphnia Toximeter". The observed effects are changes on organisms' behavior. Behavior evaluation criteria are swimming pattern, analyzed over several components, or valve opening patterns or still, the locomotion or ventilation movements and oxygen consumption, depending on used organism. Studies have shown that this evaluation can be more sensitive than traditional lethality tests, including here concentration and effect detection time. This approach allows local water resources manager to take decisions regarding its uses before an environmental accident gets out of control or even before an accident takes place. The KCI reference toxicant was used to check the functioning of the toximeter. Tests lasted 30 hours. The first 24 hours were taken for clean water exposition (dilutíon water). Thereafter, the organisms were exposed to KCI for a maximum of 2 hours, followed by a second clean water exposition to observe a possible effect reversion to a normal level. Results show that, with the conditions provided for the experiments, the toxic effect of KCI exposition was reversible and the toxic effect concentration was similar to the LC50;48h obtained with acute toxicity testing with D. similis. Such result indicates that it is possible to obtain the same results from the 48h tests in a shorter period of time and that the assay sensibility is not different from the outcomes of traditional tests. It is hoped that this research may contribute to water resources management by doing an evaluation of such a promising tool for water quality monitoring.