Toxicity of three binary mixtures to Daphnia magna: Comparing chemical modes of action and deviations from conceptual models

Abstract

Complex mixtures makes the assessment of environmental hazards difficult due to possible antagonistic or synergistic interactions that can occur between chemicals, or even more complex effect patterns like dose-level or dose-ratio-dependent responses. The aim of the present work was to investigate the acute and sublethal responses of Daphnia magna Straus exposed to four single chemical compounds (imidacloprid, thiacloprid, nickel chloride, and chlorpyrifos) and three binary chemical mixtures. In the immobilization and feeding inhibition bioassays, chlorpyrifos was the most toxic to D. magna, followed by nickel chloride, and imidacloprid and thiacloprid, which showed similar levels of toxicity. The MIXTOX was used to evaluate mixture toxicity. Observed data was compared with the expected mixture effects predicted by concentration addition (CA) and independent action (IA) models; deviations for synergistic/antagonistic interactions, dose-level and dose-ratio dependency were also used. In the mixture toxicity assessment, several patterns of response were obtained depending on the mixture but also on the endpoint tested. For imidacloprid and thiacloprid, deviations for synergism were observed in acute exposures (immobilization), and antagonism for feeding rates at sublethal concentrations. For imidacloprid and chlorpyrifos, antagonism was found in both exposures. In the nickel and chlorpyrifos case study, deviations for synergism were observed in the acute exposure; a dose-ratio deviation was observed in the feeding inhibition test, with a pattern for antagonism, except for where nickel exerts more than 60% of the mixture toxicity.

Changes of chemical chronic toxicity to Daphnia magna under different food regimes

“…Not a lot of studies assessing the chronic effects of imidacloprid to the crustacean Daphnia magna exist. Most studies with imidacloprid assess the acute toxicity after 48 h, as mentioned above, with a range of LC 50 values from 64 mg/L to 85 mg/L (Fossen, 2006;Jemec et al, 2007;Loureiro et al, 2010;Sánchez-Bayo and Goka, 2006;Song et al, 1997) and report it as relatively low compared to other neonicotinoid insecticides (Sánchez-Bayo and Goka 2006; Tomlin, 2002). On the other hand, there are several studies evaluating long-term effects of metals, like nickel, on D. magna (Evens et al, 2009;Kszos et al, 1992;Munzinger, 1990;Pane et al, 2004;Pane et al, 2003;Pavlaki et al, 2011).…”

“…In the combined toxicity tests using chemicals and food levels, the number of replicates per each treatment was decreased from ten to one to allow the use of more treatments per test, in order to obtain a broader range of the chemical's response to the combination, as advised in several studies where data is modelled using conceptual models for chemical mixtures or combination of stressors (Cedergreen et al, 2006;Cedergreen and Streibig, 2005;Ferreira et al, 2008;Jonker et al, 2004Jonker et al, , 2005Long et al, 2009;Loureiro et al, 2010;Vandenbrouck et al, 2009). Both combination sets, imidacloprid -food levels, and nickel -food levels, followed an experimental full factorial design, which included also the individual exposure tests to chemicals and food levels.…”

Challenges in risk assessment of multiple mycotoxins in food

“…In the IA model, the combined effects are estimated assuming that chemicals act independently by dissimilar MoA or at different target cells, tissues or organs and considers that the probability of toxicity from exposure to one chemical is independent from the probability of toxicity from exposure to another chemical in the mixture (Bliss, 1939;Jonker et al, 2004;Meek et al, 2011). These two reference models have found successful application to toxicological assessments of mixtures of similarly acting and dissimilarly acting compounds, both in ecotoxicology studies using a range of species (Backhaus et al, 2004;Faust et al, 2003;Loureiro et al, 2010) and in human toxicity studies using cell lines or animal models (Mueller et al, 2013;Tavares et al, 2013). Deviation from these models include synergism (mixture effect greater than additive), antagonism (mixture effect less than additive) and more subtle interactions that depend on the actual doses of the mixture components (e.g.…”

Bisphenol A migration from plastic materials: direct insight of ecotoxicity in Daphnia magna

“…Although it is recognized that organisms face multifarious mixtures of environmental stressors rather than individual chemicals at set doses and that the effects of a mixture can be very different from the sum of the contributions of the individual compounds, until now little attention has been paid to the simultaneously interaction of different pollutants and to cumulative risks, firstly highlighted in the Framework for Cumulative Risk Assessment of USEPA (2003). This led to the concern that testing of single chemicals may completely underestimate effects in mixtures, leading to the erroneous conclusion that no effects are observed, whereas in fact, effects would be expected in the field environment where animals are exposed to mixtures (Kortenkamp et al 2012;Loureiro et al 2010;Barata et al 2006).…”