Mixture toxicity of wood preservative products in the fish embryo toxicity test

Comparison of imidacloprid, propiconazole, and nanopropiconazole effects on the development, behavior, and gene expression biomarkers of the Pacific oyster (Magallana gigas)

Coastal areas are final recipients of various contaminants including pesticides. The effects of pesticides on non-target organisms are often unclear, especially at environmentally relevant concentrations. This study investigated the impacts of insecticide imidacloprid (IMI) and fungicide propiconazole (PRO), some of the most detected pesticides in the Arcachon Bay in France. This work also included the research of propiconazole nanoformulation (nanoPRO). The effects were assessed studying the development of the early life stages of the Pacific oyster (Magallana gigas). Oyster embryos were exposed for 24, 30, and 42 h (depending on the endpoint) at 24 °C to environmentally relevant concentrations of the two pesticides as well as to nanoPRO. The research focused on sublethal endpoints such as the presence of developmental malformations, alterations of locomotion patterns, or changes in the gene expression levels. No developmental abnormalities were observed after exposure to environmental concentrations detected in the Arcachon Bay in recent years (maximal detected concentration of IMI and PRO were 174 ng/L and 29 ng/L, respectively). EC₅₀ of PRO and nanoPRO were comparable, 2.93 ± 1.35 and 2.26 ± 1.36 mg/L, while EC₅₀ of IMI exceeded 200 mg/L. IMI did not affect larval behavior. PRO affected larval movement trajectory and decreased average larvae swimming speed (2 μg/L), while nanoPRO increased the maximal larvae swimming speed (0.02 μg/L). PRO upregulated especially genes linked to reactive oxygen species (ROS) production and detoxification. NanoPRO effects on gene expression were less pronounced - half of the genes were altered in comparison with PRO. IMI induced a strong dose-response impact on the genes linked to the detoxification, ROS production, cell cycle, and apoptosis regulation. In conclusion, our results suggest that current pesticide concentrations detected in the Arcachon Bay are safe for the Pacific oyster early development, but they might have a small direct effect via altered gene expressions, whose longer-term impacts cannot be ruled out.

Diazepam, metformin, omeprazole and simvastatin: a full discussion of individual and mixture acute toxicity

High consumption of drugs, combined with their presence in the environment, raises concerns about its consequences. Even though researches are often engaged in analyzing substances separately, that is not the environmental reality. Therefore, the aim of this study was to investigate the acute toxicity of the pharmaceuticals simvastatin, metformin, omeprazole and diazepam, and all possible mixtures between them, to the organism Aliivibrio fischeri, verifying possible synergistic or antagonistic effects and assessing byproducts formation. In terms of individual toxicity, omeprazole is the most toxic of the active ingredients, followed by simvastatin, diazepam and, finally, metformin. When the toxicity of mixtures was tested, synergism, antagonism and hormesis were perceived, most probably generated due to byproducts formation. Moreover, it was observed that even when compounds are at concentrations below the non-observed effect concentration (NOEC), there may be toxicity to the mixture. Hence, this work points to the urgent need for more studies involving mixtures, since chemicals are subject to interactions and modifications, can mix, and potentiate or nullify the toxic effect of each other.

Dose-response analysis of toxicological and pharmacological mixtures with the model deviation ratio method: Problems and solutions

Risk assessment for mixtures of chemicals requires to investigate the magnitude of their potential adverse effects on living organisms. This is usually done by assessing how experimental toxicological mixture data depart from the model of Loewe additivity. Several recent scientific studies propose to perform this task using an ad hoc method known as model deviation ratio (MDR) method. Moreover, the first official European regulatory document for the study of combined exposures explicitly recommends the use of the MDR method (EFSA Scientific Committee et al. Guidance on harmonised methodologies for human health, animal health and ecological risk assessment of combined exposure to multiple chemicals. EFSA Journal, 2019). We show here that the MDR method is not rooted in statistical principles and can lead to erroneous claims. We show however that the distribution of the MDR can be evaluated by simulations and show how this allows us to devise and carry out a bona fide statistical test. The proposed method accounts for uncertainty in the estimation of ED/EC50 and does not require a minimum sample size. The computer code developped in this study is made available as an R package called MDR.

Mixture toxicity assessment of a biocidal product based on reproduction and avoidance behaviour of the collembolan Folsomia candida

Biocidal products represent mixtures that might be released into the environment at application and continuously during service life. Concentration addition (CA) has been proposed as default model to calculate theoretical mixture toxicity. However, the suitability of CA for chronic toxicity towards soil organisms has so far rarely been evaluated and therefore needs further experimental evidence. The present study investigated the toxicity of a wood preservative product and the individual active substances (tebuconazole and IPBC) therein with the aim to evaluate the compliance with the CA prediction for the product. Folsomia candida was selected as test organism for this purpose using the endpoints reproduction and avoidance behaviour. Both endpoints were increasingly impacted by increasing concentrations of the wood preservative product as well as its active substances tested individually. The chronic effects of the product could be predicted by CA with less than 4-fold deviation, while the assessment for avoidance behaviour indicated a strong underestimation. This underestimation could not be attributed to the one known formulation additive, an organic solvent. Overall, the present study provides some more evidence that CA could be applied as default model for standard endpoints of soil organisms, but warns against using CA for behavioural responses.

Toxic evaluations of sediments in Tokyo Bay, Japan, using Japanese medaka embryos

Toxic risks of sediments collected from seven sites in Tokyo Bay were evaluated using Japanese medaka embryos. Those sediments with slight pore water were placed in grass petri dishes without overlying water. The most remarkable effect in the field sediment was to cause hatching delay in embryos, and the longest time until hatching took was 12.5 ± 1.6 days post-fertilization (dpf), although that in control group was 10.1 ± 0.7 dpf. A significant delay in hatching was observed at four sites. Because total carbon concentrations were relatively high in sediments at three of these four sites, several chemicals were expected to be residues in these sites and could cause their delay. Although extreme mortality was not observed at all sites, sediments collected from the site close to Kawasaki city induced 10 % mortality. Polycyclic aromatic hydrocarbon (PAH) concentrations were remarkably high at this site compared with other sites, and thus PAH toxicities could be causing the mortality. Concentration of heavy metals such as cadmium, copper, lead, and zinc in sediments were also determined, but no clear relationship was found between toxicities to embryos and the distribution of their concentrations.

Mixture toxicity of water contaminants-effect analysis using the zebrafish embryo assay (Danio rerio)

Three water contaminants were selected to be tested in the zebrafish embryo toxicity test (DarT) in order to investigate the sensitivity of the zebrafish embryo toxicity test with respect to mixture effect detection. The concentration-response curves for the observed effects lethality and hypo-pigmentation were calculated after an exposure of the embryos for 96 h with a fungicide (carbendazim), a plasticizer or propellent precursor (2,4-DNT: 2,4- dinitrotoluene) and an aromatic compound (AαC: 2-amino-9H-pyrido[2,3-b]indol), respectively. Follow-up mixture tests were based on the calculated LC50 or EC50 of the single compounds and combined effects were predicted according to the mixture concepts of concentration addition (CA) and independent action (IA). The order of toxicity for the single substances was carbendazim (LC50 = 1.25 μM) < AαC (LC50 = 8.16 μM) < 2,4-DNT (LC50 = 177.05 μM). For AαC and 2,4 DNT hypo-pigmentation was observed in addition (AαC EC50 = 1.81 μM; 2,4-DNT EC50 = 8.81 μM). Two binary and one ternary mixture were studied on lethality and one on hypo-pigmentation: 2,4-DNT/AαC (LC50 = 119.21 μM, EC50 = 5.37 μM), carbendazim/AαC (LC50 = 4.49 μM) and AαC/Carbendazim/2,4 DNT (LC50 = 108.62 μM). Results showed that the effects were in agreement with the CA model when substances were tested in mixtures. Therefore, in a reasonable worst case scenario substance combination effects in fish embryos were at maximum only prone to overestimation when using CA as the mixture concept.

Time-dependence in mixture toxicity prediction

The value of time-dependent toxicity (TDT) data in predicting mixture toxicity was examined. Single chemical (A and B) and mixture (A+B) toxicity tests using Microtox(®) were conducted with inhibition of bioluminescence (Vibrio fischeri) being quantified after 15, 30 and 45-min of exposure. Single chemical and mixture tests for 25 sham (A1:A2) and 125 true (A:B) combinations had a minimum of seven duplicated concentrations with a duplicated control treatment for each test. Concentration/response (x/y) data were fitted to sigmoid curves using the five-parameter logistic minus one parameter (5PL-1P) function, from which slope, EC25, EC50, EC75, asymmetry, maximum effect, and r(2) values were obtained for each chemical and mixture at each exposure duration. Toxicity data were used to calculate percentage-based TDT values for each individual chemical and mixture of each combination. Predicted TDT values for each mixture were calculated by averaging the TDT values of the individual components and regressed against the observed TDT values obtained in testing, resulting in strong correlations for both sham (r(2)=0.989, n=25) and true mixtures (r(2)=0.944, n=125). Additionally, regression analyses confirmed that observed mixture TDT values calculated for the 50% effect level were somewhat better correlated with predicted mixture TDT values than at the 25 and 75% effect levels. Single chemical and mixture TDT values were classified into five levels in order to discern trends. The results suggested that the ability to predict mixture TDT by averaging the TDT of the single agents was modestly reduced when one agent of the combination had a positive TDT value and the other had a minimal or negative TDT value.

Predicting acute and chronic effects of wood preservative products in Daphnia magna and Pseudokirchneriella subcapitata based on the concept of concentration addition

The current European legislation requires that combined effects of the active substances and any substance of concern contained in biocidal products are taken into account in environmental risk assessment. The hypothesis whether the consideration of active substances together with all formulation additives that are labeled as presenting an environmental hazard is sufficient for a reliable environmental risk assessment was tested in the present study by investigating 3 wood preservative products. Relevant single substances in the products, some of their generic mixtures, the biocidal products themselves, and aqueous eluates prepared from the products (representing potential environmental mixtures) were tested for effects on algal growth and Daphnia acute immobilization as well as reproduction. Predictions for the products and the eluates were based on the concept of concentration addition and were mostly found to provide reliable or at least protective estimates for the observed acute and chronic toxicity of the mixtures. The mixture toxicity considerations also indicated that the toxicity of each product was dominated by just 1 of the components, and that assessments based only on the dominating substance would be similarly protective as a full-mixture risk assessment. Yet, there remained uncertainty in some cases that could be related to the toxicity of transformation products, the impact of unidentified formulation additives, or synergistic interaction between active substances and formulation additives.