Influence of soil organic matter on the sensitivity of selected wild and crop species to common herbicides

Comparative assessment of the intrinsic sensitivity of crop species and wild plant species to plant protection products and their active substances and potential implications for the risk assessment: A literature review

A comprehensive critical review was undertaken aiming to compare the intrinsic sensitivity of terrestrial plant species (crop species and noncrop wild species) with published literature and unpublished proprietary data generated for the registration of plant protection products (PPPs), and a database was compiled. Data were assessed to answer the question whether crops differ from noncrop plants in their intrinsic sensitivity to PPPs. Endpoints were assessed considering further potentially relevant parameters by means of different methods, including a quotient approach, in which overall crop endpoints were divided by matching wild species endpoints. Quotients above 1 indicated that wild species were more sensitive than crops, quotients below 1 the opposite. Further methods included a multiple regression analysis and different approaches to assess the statistical power. The overall finding was that there were no consistent differences in sensitivity between wild plant species and crop species, based on ER50, ER25, and ER10 vegetative endpoints (the largest fraction of data). This was also true when censored endpoints, seedling emergence data, and other measured variables such as shoot height were included. Statistically significant differences occurred in both directions and were balanced, that is, there was no clear trend for either crops or noncrop species to be more sensitive than the other. On the basis of multivariate regression analysis, crops were found to be significantly more sensitive than wild plant species, albeit by a small margin (factor ≈1.4). Minimum detectable difference (MDD) analysis and multivariate regression analysis of modified datasets indicated that when using a data set of this size and heterogeneity, any dissimilarity between crop and wild species was detectable if exceeding a factor of 1.4 in either direction. For the taxonomic groups assessed here (i.e., with data), no intrinsic difference in sensitivity to PPPs between crop species and wild plant species was found. Integr Environ Assess Manag 2019;15:176-189. © 2018 SETAC.

Can nano-SiO2 reduce the phytotoxicity of acetaminophen? - A physiological, biochemical and molecular approach

This study aimed at evaluating the interactive effects of acetaminophen (AC; 400 mg kg^-1) and silicon dioxide nanomaterial (nano-SiO₂;3 mg kg^-1) on soil-grown barley. After 14 days of growth, plant growth, evaluated in terms of fresh and dry weight, was greatly inhibited by AC, independently of being or not co-treated with nano-SiO₂. Plants growing under high levels of AC did not show any increase in malondialdehyde (MDA) nor thiols contents, though levels of superoxide anion (O₂^.-) and hydrogen peroxide (H₂O₂) were increased in leaves and roots, respectively. When plants were co-treated with nano-SiO₂, reactive oxygen species (ROS) content remained unchanged, but lipid peroxidation (LP) was diminished and the thiol redox network was up-regulated in roots. The evaluation of the response of the antioxidant system showed that AC affected both non-enzymatic and enzymatic components in an organ-specific manner: proline levels and superoxide dismutase (SOD) activity were enhanced, whilst catalase (CAT) activity decreased in leaves; ascorbate content and CAT activity were diminished in roots. In response to the nano-SiO₂ co-treatment, this pattern was not vastly altered, despite for ascorbate peroxidase (APX), whose activity was greatly enhanced in both organs. Overall, combining biometric, biochemical and molecular approaches, this study revealed that, although AC impaired plant growth and development, it did not trigger a harsh oxidative stress condition. Maybe by this reason, the ameliorating potential of nano-SiO₂ was not so evident; yet, nano-SiO₂ was able to reduce LP and to stimulate thiol content and APX activity, possibly as a defense mechanism against AC-induced stress.

Herbicide Toxicity Testing with Non-Target Boreal Plants: The Sensitivity of Achillea millefolium L. and Chamerion angustifolium L. to Triclopyr and Imazapyr

Terrestrial plant toxicity tests were conducted to determine the sensitivity of two boreal plants, yarrow (Achillea millefolium L.) and fireweed (Chamerion angustifolium L.), to the herbicides imazapyr and triclopyr. Both plants are common non-target species on northern powerline rights-of-way where the impacts of proposed herbicide applications are of concern. In the vegetative vigour test, triclopyr foliar spray caused extensive damage to A. millefolium at <50% of the maximum field application rate (inhibition concentration (IC)₅₀ = 1443.8 g a.i. ha^-1) and was lethal to C. angustifolium at the lowest dose tested (1210.9 g a.i. ha^-1). Both species demonstrated extremely high sensitivity to imazapyr foliar spray: IC_50s = 8.29 g a.i. ha^-1 and 4.82 g a.i. ha^-1 (<1.5% of the maximum field rate). The seedling emergence and seedling growth tests were conducted in the organic horizon of five boreal soils. Few differences in herbicide bioavailability between soils were detected. Triclopyr limited growth of A. millefolium, C. angustifolium and standard test species Calamagrostis canadensis at low levels (most IC₅₀ estimates between 2-20 µg g^-1). For imazapyr, IC₅₀ estimates could not be calculated as there was >75% inhibition of endpoints at the lowest doses of ~2 µg g^-1. A foliar application of triclopyr or imazapyr for woody species control would likely cause significant damage to boreal non-target plants. The high sensitivity of both species to herbicide residues in soil indicates long term impacts are dependent on herbicide degradation rates in northern conditions. A. millefolium performed well and is recommended for use in toxicity testing relevant to boreal regions.

Ecotoxicological relevance of nano-NiO and acetaminophen to Hordeum vulgare L.: Combining standardized procedures and physiological endpoints

The present work aimed to assess the ecotoxicological relevance of acetaminophen (AC) and nickel oxide nanomaterial (nano-NiO) to barley plants. Combining standard procedures and several biochemical determinations, a global approach regarding the biological effects of these two contaminants was performed. After 14 days of growth, the exposure of barley to increased concentrations (0, 87.8, 131.3, 197.5, 296.5, 444.4, 666.6, and 1000 mg kg^-1) of each contaminant resulted in a marked decrease in biomass production and biometric parameters. Photosynthetic pigments and markers of oxidative stress were analyzed to assess if any of the treatments interfered with the physiological performance and with the cellular redox state. Our observations revealed that only nano-NiO induced a negative response in total chlorophylls and carotenoids, confirming the macroscopic phytotoxicity symptoms (chlorosis). However, both contaminants led to a significant increase in lipid peroxidation (LP), superoxide anion (O₂^.-), and cell death for all the tested concentrations, suggesting that AC and nano-NiO cause oxidative stress in barley, even at the lowest applied dose (87.8 mg kg^-1). Comparing the two studied approaches (parameters included in standard protocols and several biochemical determinations), it is concluded that the inclusion of several biochemical endpoints, especially those related to oxidative stress, resulted in a more sensitive analysis and thus, a more sensitive risk evaluation of these two contaminants for barley plants.