Comparative toxicities of fungicide and herbicide formulations on freshwater and marine species

Fungicides: An Overlooked Pesticide Class?

Fungicides are indispensable to global food security and their use is forecasted to intensify. Fungicides can reach aquatic ecosystems and occur in surface water bodies in agricultural catchments throughout the entire growing season due to their frequent, prophylactic application. However, in comparison to herbicides and insecticides, the exposure to and effects of fungicides have received less attention. We provide an overview of the risk of fungicides to aquatic ecosystems covering fungicide exposure (i.e., environmental fate, exposure modeling, and mitigation measures) as well as direct and indirect effects of fungicides on microorganisms, macrophytes, invertebrates, and vertebrates. We show that fungicides occur widely in aquatic systems, that the accuracy of predicted environmental concentrations is debatable, and that fungicide exposure can be effectively mitigated. We additionally demonstrate that fungicides can be highly toxic to a broad range of organisms and can pose a risk to aquatic biota. Finally, we outline central research gaps that currently challenge our ability to predict fungicide exposure and effects, promising research avenues, and shortcomings of the current environmental risk assessment for fungicides.

Effect of New Thiophene-Derived Aminophosphonic Derivatives on Growth of Terrestrial Plants. Part 2. Their Ecotoxicological Impact and Phytotoxicity Test Toward Herbicidal Application in Agriculture

Background: The aim of this work was to evaluate phytotoxicity of the thiophene derivatives against three persistent weeds of a high degree of resistance (Galinsoga parviflora Cav., Rumex acetosa L., and Chenopodium album) as well as their ecotoxicological impact on Heterocypris incongruens. In addition, Aliivibrio fischeri was measured. Two of eight described aminophosphonates, namely dimethyl N-(2-methoxyphenyl)amino(2-thienyl)methylphosphonate (2d) and dimethyl N-(tert-butyl)- (2-thienyl)methylphosphonate (2h), have never been reported before. Methods: The phytotoxicity of tested aminophosphonates toward their potential application as soil-applied herbicides was evaluated according to the OECD 208 Guideline. Ecotoxicological properties of investigated compounds were made using the OSTRACODTOXKIT^TM and Microtox^® tests. Results: Obtained results showed that four aminophosphonates have interesting herbicidal properties and N-(2-methylphenyl)amino- (2-thienyl)methylphosphonate (2a) was found to kill efficiently the most resistant plant Chenopodium album. None of the tested compounds showed important toxicity against Aliivibrio fischeri. However, their toxic impact on Heterocypris incongruens was significantly elevated. Conclusions: The aminophosphonate 2a showed herbicidal potential and it is not toxic against tested bacteria (EC₅₀ over 1000 mg/L). It was found to be moderately toxic against ostracods [mortality 48% at 10 mg/kg of soil dry weight (s.d.w.)] and this problem should be solved by the use of the controlled release from a polymeric carrier.

Vibrio fischeri bioluminescence inhibition assay for ecotoxicity assessment: A review

Vibrio fischeri bioluminescence inhibition bioassay (VFBIA) has been widely applied for the monitoring of toxicity on account of multiple advantages encompassing shorter test duration, sensitive, cost-effective and ease of operation. Moreover, this bioassay found to be equally applicable to all types of matrices (organic & inorganic compounds, metals, wastewater, river water, sewage sludge, landfill leachate, herbicides, treated wastewater etc.) for toxicity monitoring. This review highlights the apparent significance of Vibrio fischeri bioluminescence inhibition assay for ecotoxicological screening and evaluation of diverse chemical substances toxicity profile. The biochemical and genetic basis of the bioluminescence assay and its regulatory mechanism have been concisely discussed. The basic test protocol with ongoing improvements, widespread applications, typical advantages and probable limitations of the assay have been overviewed. The sensitivity of VFBIA and toxicity bioassays has also been compared.

Novel (5-nitrofurfuryl)-substituted esters of phosphonoglycine - Their synthesis and phyto- and ecotoxicological properties

Since aminophosphonate-based herbicides like glyphosate are currently one of the most popular and widely applied active agent in agrochemistry, there is an urgent need for searching new compounds among this family with potential herbicidal activity, but exhibiting low toxicity against surrounding environment. Six new (5-nitrofurfuryl)-derived aminophosphonates were synthesized for the first time and apart from the only one example of N-benzylamino(5-nitrofuryl)-methylphosphonic acid, it was the first time in the history, when this class of compounds was prepared. Their prospective and real biological properties have been followed up by evaluation of their preliminary ecotoxicology. They have been then investigated in aspect of their phytotoxicity against oat (A. sativa) and common radish (R. sativus) exhibiting moderate-to-severe toxicity for these plants. The significant selectivity towards radish (up to 3 times greater toxicity against radish) was observed in some cases. Title compounds were also tested in terms of their toxicity for freshwater crustaceans H. incongruens (ostracods) and marine luminescent bacteria A. fischeri. Although their harmful action on ostracods was not too much elevated, they were found to be highly toxic for bacteria. Various aspects of their ecotoxicity are discussed in this paper.

Critical assessment of pendimethalin in terms of persistence, bioaccumulation, toxicity, and potential for long-range transport

Pendimethalin (PND, CAS registry number 40487-42-1) is a dinitroaniline herbicide that selectively controls broad-leaf and grassy weeds in a variety of crops and in noncrop areas. It has been on the market for about 30 yr and is currently under review for properties related to persistence (P), bioaccumulation (B), and toxicity (T) in the European Union (EU). A critical review of these properties as well as potential for long-range transport (LRT) was conducted. Pendimethalin has a geometric mean (GM) half-life of 76-98 d in agriculturally relevant soils under aerobic conditions in the lab. The anaerobic half-life was 12 d. The GM for field half-lives was 72 d. The GM half-life for sediment-water tests in the lab was 20 d and that in field aquatic cosms ranged from 45 to 90 d. From these data PND is not persistent as defined in the Annex II of EC regulation 1107/2009. The GM bioconcentration factor for PND was 1878, less than the criterion value. This was consistent with lack of biomagnification or accumulation in aquatic and terrestrial food chains. The GM no-observed-effect concentration (NOEC) value for fish was 43 µg/L, and 11 µg/L for algae. These do not trigger the criterion value for toxicity. In air, the DT50 of PND was estimated to be 0.35 d, which is well below the criterion of 2 d for LRT under the United Nations Economic Commission for Europe (UNECE) Aarhus protocol. Modeling confirmed lack of LRT. Because of its volatility, PND may be transported over short distances in air and was found in samples in local and semiremote regions; however, these concentrations are not of toxicological concern. Unlike other current-use pesticides, PND has not been found in samples from remote regions since 2000 and there is no apparent evidence that this herbicide accumulates in food chains in the Arctic.

Individual and joint toxicity of the herbicide S-metolachlor and a metabolite, deethylatrazine on aquatic crustaceans: Difference between ecological groups

We studied the individual and joint acute toxicity of S-metolachlor (SMOC) and deethylatrazine (DEA - a metabolite of atrazine) on different non-target freshwater crustaceans. We used animals from different ecological groups: two amphipods from surface running water (Gammarus pulex and Gammarus cf. orinos), an isopod from surface stagnant water (Asellus aquaticus) and an amphipod living in groundwater (Niphargus rhenorhodanensis). Organisms were exposed to different levels of SMOC and DEA, alone or in binary mixture. Temperature effect on SMOC toxicity was assessed by exposing G. pulex and N. rhenorhodanensis to SMOC at 11 °C and 15 °C. Studying mortality as the biological endpoint, N. rhenorhodanensis was more resistant than surface water species towards SMOC and DEA. Among surface water species, G. pulex was the most sensitive while Gammarus cf. orinos and A. aquaticus showed similar responses to both compounds. Temperature increase did not change SMOC toxicity but modify the shape and steepness of the dose-response curve. We used a Model Deviation Ratio (MDR) approach to evaluate the predictability of Concentration Addition (CA) and Independent Action (IA) models to mixture toxicity. Results indicated either an additive or an antagonistic or a synergistic interaction depending on the concentrations combination and the test species. Our finding conclusively show the suitability of CA and IA in predicting mixture toxicities but results should be interpreted with caution according to ecological group of exposed species in risk assessment procedures.

The effects of a fungicide and chytrid fungus on anuran larvae in aquatic mesocosms

The amphibian disease chytridiomycosis, caused by the pathogenic fungus Batrachochytrium dendrobatidis (Bd), has been linked to significant amphibian declines over the past three decades. The most severe effects of the pathogen have been primarily observed in relatively pristine areas that are not affected by many anthropogenic factors.One hypothesis concerning improved amphibian persistence with Bd in disturbed landscapes is that contaminants may abate the effects of Bd on amphibians. Recent laboratory studies have shown that pesticides, specifically the fungicide thiophanate-methyl (TM), can kill Bd outside of hosts and clear Bd infections within hosts. Using aquatic mesocosms, we tested the hypothesis that TM (0.43 mg/L) would alter growth and development of Lithobates sphenocephalus (southern leopard frog) tadpoles and Bd-infection loads in infected individuals. We hypothesized that the scope of such alterations and infection clearing would be affected by aquatic community variables, specifically zooplankton. TM altered zooplankton diversity (reduced cladoceran and increased copepod and ostracod abundances) and caused mortality to all tadpoles in TM-exposed tanks. In TM-free tanks, Bd-exposed tadpoles in high-density treatments metamorphosed smaller than Bd-unexposed, effects that were reversed in low-density treatments. Our study demonstrates the potential adverse effects of a fungicide and Bd on tadpoles and aquatic systems.

Validation and extension of a similarity-based approach for prediction of acute aquatic toxicity towards Daphnia magna

Quantitative structure-activity relationship (QSAR) models for predicting acute toxicity to Daphnia magna are often associated with poor performances, urging the need for improvement to meet REACH requirements. The aim of this study was to evaluate the accuracy, stability and reliability of a previously published QSAR model by means of further external validation and to optimize its performance by means of extension to new data as well as a consensus approach. The previously published model was validated with a large set of new molecules and then compared with ChemProp model, from which most of the validation data were taken. Results showed better performance of the proposed model in terms of accuracy and percentage of molecules outside the applicability domain. The model was re-calibrated on all the available data to confirm the efficacy of the similarity-based approach. The extended dataset was also used to develop a novel model based on the same similarity approach but using binary fingerprints to describe the chemical structures. The fingerprint-based model gave lower regression statistics, but also less unpredicted compounds. Eventually, consensus modelling was successfully used to enhance the accuracy of the predictions and to halve the percentage of molecules outside the applicability domain.

Quantification of toxic effects of the herbicide metolachlor on marine microalgae Ditylum brightwellii (Bacillariophyceae), Prorocentrum minimum (Dinophyceae), and Tetraselmis suecica (Chlorophyceae)

Toxic effects of the herbicide metolachlor (MC) were evaluated for three marine microalgae, Tetraselmis suecica (chlorophyte), Ditylum brightwellii (diatom), and Prorocentrum minimum (dinoflagellate). MC showed a significant reduction in cell counts and chlorophyll a levels. Median effective concentration (EC50) was calculated based on chlorophyll a levels after a 72-h MC exposure. EC50 values for T. suecica, D. brightwellii, and P. minimum were 21.3, 0.423, and 0.07 mg/L, respectively. These values showed that the dinoflagellate was most sensitive when exposed to the herbicide, at a concentration comparable to freshwater algae, suggesting its potential as an appropriate model organism for ecotoxicity assessments in marine environments.

Toxicity of cadmium, lead, mercury and methyl parathion on Euchlanis dilatata Ehrenberg 1832 (Rotifera: Monogononta)

Acute toxicity tests with Cd, Pb, Hg, and methyl parathion were developed to compare the sensitivity of the rotifer Euchlanis dilatata with other model organisms used in aquatic ecotoxicology. Cd was the most toxic chemical (LC50 = 14.8 μg L(-1)), while methyl parathion was the least toxic (LC50 = 864.2 μg L(-1)). E. dilatata was more sensitive that other rotifer species, particularly of the genera Brachionus and Lecane. However, E. dilatata was less sensitive to mercury and methyl parathion than the crustacean, Daphnia magna. The high sensitivity of E. dilatata suggests that it may be an adequate benthic model to use in toxicity assessments of metal-contaminated sediments.