Plastic Fruit Stickers in Industrial Composting─Surface and Structural Alterations Revealed by Electron Microscopy and Computed Tomography.

Often large quantities of plastics are found in compost, with price look-up stickers being a major but little-explored component in the contamination path. Stickers glued to fruit or vegetable peels usually remain attached to the organic material despite sorting processes in the composting plant. Here, we investigated the effects of industrial composting on the structural alterations of these stickers. Commercial polypropylene (PP) stickers on banana peels were added to a typical organic material mixture for processing in an industrial composting plant and successfully resampled after a prerotting (11 days) and main rotting step (25 days). Afterward, both composted and original stickers were analyzed for surface and structural changes via scanning electron microscopy, Fourier-transform infrared spectroscopy, and micro- and nano-X-ray computed tomography (CT) combined with deep learning approaches. The composting resulted in substantial surface changes and degradation in the form of microbial colonization, deformation, and occurrence of cracks in all stickers. Their pore volumes increased from 16.7% in the original sticker to 26.3% at the end of the compost process. In a similar way, the carbonyl index of the stickers increased. Micro-CT images additionally revealed structural changes in the form of large adhesions that penetrated the surface of the sticker. These changes were accompanied by delamination after 25 days of composting, thus overall hinting at the degradation of the stickers and the subsequent formation of smaller microplastic pieces.

18O Isotope Labeling Combined with 31P Nuclear Magnetic Resonance Spectroscopy for Accurate Quantification of Hydrolyzable Phosphorus Species in Environmental Samples.

31P nuclear magnetic resonance (NMR) spectra can be biased due to the hydrolysis of labile P species during sample treatment and NMR analysis. This paper offers an approach to circumvent this problem by performing sample preparation and analysis in 18O-enriched medium. Heavy 18O isotope atoms were introduced into the resulting artificial hydrolysis products. The NMR signal of 18O-labeled P was shifted upfield relative to the unlabeled P nuclei in natural metabolites. This isotope shift enabled an immediate differentiation of artificial hydrolysis products from natural metabolites. Moreover, the hydrolysis products could be accurately quantified. Our data suggest that the extent to which artificial hydrolysis alters NMR spectra varies among different types of environmental samples. For instance, 72-84% of the detected monoesters in the organic soils of this study were actually artificially hydrolyzed diesters. By contrast, artificial hydrolysis products in the mineral soils used for this study accounted for less than 6% of the total monoesters. Polyphosphate was also hydrolyzed to yield 18O-labeled products in algal biomass.

Multiresidue determination of pesticides in acid-clay soils from Thailand.

Tropical and temperate soils differ with respect to their chemical conditions and mineral composition. Consequently, assessment of the contamination of tropical soils with pesticides requires methods that provide exhaustive extraction from the specific soil matrix and reliable quantification. Our objective was to optimize the simultaneous extraction and determination of 32 representative pesticides (organophosphates, organochlorines, synthetic pyrethroids, triazines, acetamides, carbamates, diphenyl ethers, acylalanines, oxadiazoles, thiadiazoles, and phenoxy compounds) frequently used in Thailand. The compounds were added to a clayey Ultisol-topsoil (45% clay) from the Yom Region in Northern Thailand. Ten different solvent mixtures were tested; the use of a shake extraction with acetone-ethyl acetate-water (3 + 1 + 1, v/v/v) was most effective in providing exhaustive and reproducible extraction of pesticides both from freshly fortified soil and from fortified soil after incubation for 14-28 days. The pesticides were separated and quantified by using gas chromatography with mass selective detection. Except for methamidophos, which was almost completely lost during sample workup, the recoveries of all pesticides from soil ranged from 68.6 to 104% (mean standard error, 2.8%) for freshly spiked samples and from 45.9 to 107% (mean standard error, 2.3%) for spiked samples incubated for 14 days. The use of internal standards compensated for the losses of most pesticides during workup and increased the mean recovery of the pesticides from freshly fortified soil to 96%. The method was successfully applied to the determination of environmental concentrations of pesticides in a range of Thai agricultural soils.

Sorption and aging of corn and soybean pesticides in tropical soils of Brazil.

The efficacy and fate of pesticides in soil strongly depend on sorption reversibility that is known to decrease with increasing contact time (aging). We elucidated the aging dynamics of eight different pesticides in two contrasting agricultural soils of tropical Brazil (Ustox and Psamments), using batch equilibrium experiments and sequential extractions of field samples. Adsorption was best described by Langmuir isotherms for the entire and by Freundlich equations for the lower concentration range. In field samples, water extractable pesticide fractions mostly dissipated at least twice as fast as did the solvent extractable fractions. Hence, in comparison to 0 days K(OC) values, measured field K(OC) values were higher by a factor of 2.6-38 for the clayey Ustox and 2.1-72 for the sandy Psamments toward the end of the experimental period at 80 days after application. The extent of such aging basically increased with increasing polarity of the pesticide. An absolute enrichment of polar pesticides within the final exhaustive acetone--ethyl acetate--water extracts was observed during the experimental period, so that we may deduce that pesticides had redistributed into stronger sorption sites. The time course of the K(OC) development was well-described using a semiempirical equation, which had been employed for temperate soils before.

Pesticides in surface water, sediment, and rainfall of the northeastern Pantanal basin, Brazil.

Within the last 25 years an intensive agriculture has developed in the highland regions of Mato Grosso state (Brazil), which involves frequent pesticide use in highly mechanized cash-crop cultures. To provide information on pesticide distribution and dynamics in the northeastern Pantanal basin (located in southern Mato Grosso), we monitored 29 pesticides and 3 metabolites in surface water, sediment, and rainwater of the study area during the main application season. In environmental samples, 19 pesticides and 3 metabolites were detected in measurable quantities, resulting in at least one pesticide detection in 68% of surface water samples (n = 139), 62% of sediment samples (n = 26), and 87% of rainwater samples (n = 91). Surface water samples were most frequently contaminated by endosulfan compounds (alpha-, beta-, -sulfate), ametryn, metolachlor, and metribuzin, although in low (< 0.1 microgram L-1) concentrations. Sediment samples exhibited concentrations up to 4.5 micrograms kg-1 of p,p'-DDT, p,p'-DDE, endosulfan-sulfate, beta-endosulfan, and ametryn. In contrast, rainwater was polluted with substantial amounts of endosulfan, alachlor, metolachlor, trifluralin, monocrotofos, and profenofos (maximum concentrations = 0.3 to 2.3 micrograms L-1) in the highlands. Lowland rainwater samples taken 75 km from the next application area contained 5- to 10-fold lower mean pesticide concentration than in the highlands. Cumulative deposition rates of the pesticide sum within the study period ranged from 423 micrograms m-2 in the highlands to 14 micrograms m-2 in the lowlands. The atmospheric input of pesticides to ecosystems seemed to be of higher relevance in the tropical study area than known from temperate regions.

Fate of (14)C-labeled soybean and corn pesticides in tropical soils of Brazil under laboratory conditions.

The dissipation rate of seven currently used soybean and corn pesticides in two tropical soils (Ustox and Psamments) of Brazil was studied in a laboratory incubation experiment. Dissipation half-lives of pesticides ranged between 2 (monocrotofos) and 90 days (endosulfan-beta). The contrasting clay contents of the studied tropical soils (130 versus 470 g of clay kg(-1) of soil) did not influence the dissipation dynamics of pesticides substantially. Mineralization to CO(2) was high [up to 78% of the applied radioactivity (AR)] for the studied organophosphorus compounds and deltamethrin, which also formed considerable amounts of bound residues (>20% of AR) during the 80 days of incubation. The highest portion of nonextractable residues was found for alachlor and simazine (55-60% of AR). In contrast, the nonpolar trifluralin and endosulfan formed only small amounts of bound residues (mostly <20% of AR) but showed the highest dissipation half-lives (>14 days) in the studied soils, also due to a low mineralization rate. When endosulfan-sulfate, as the main metabolite of endosulfan, was considered, the half-life time of endosulfan compounds (sum of -alpha, -beta, and -sulfate) was enhanced to >160 days in both soils. In comparison with the laboratory experiments, dissipation half-life times of chlorpyrifos, endosulfan-alpha, and trifluralin were shortened by a factor of 10-30 in field trials with the same soils, which was related to the volatilization potential of pesticides from soils.