Subsidy Quality Affects Common Riparian Web-Building Spiders: Consequences of Aquatic Contamination and Food Resource

Anthropogenic stressors can affect the emergence of aquatic insects. These insects link aquatic and adjacent terrestrial food webs, serving as high-quality subsidy to terrestrial consumers, such as spiders. While previous studies have demonstrated that changes in the emergence biomass and timing may propagate across ecosystem boundaries, the physiological consequences of altered subsidy quality for spiders are largely unknown. We used a model food chain to study the potential effects of subsidy quality: Tetragnatha spp. were exclusively fed with emergent Chironomus riparius cultured in the absence or presence of either copper (Cu), Bacillus thuringiensis var. israelensis (Bti), or a mixture of synthetic pesticides paired with two basal resources (Spirulina vs. TetraMin®) of differing quality in terms of fatty acid (FA) composition. Basal resources shaped the FA profile of chironomids, whereas their effect on the FA profile of spiders decreased, presumably due to the capacity of both chironomids and spiders to modify (dietary) FA. In contrast, aquatic contaminants had negligible effects on prey FA profiles but reduced the content of physiologically important polyunsaturated FAs, such as 20:4n-6 (arachidonic acid) and 20:5n-3 (eicosapentaenoic acid), in spiders by approximately 30% in Cu and Bti treatments. This may have contributed to the statistically significant decline (40%-50%) in spider growth. The observed effects in spiders are likely related to prey nutritional quality because biomass consumption by spiders was, because of our experimental design, constant. Analyses of additional parameters that describe the nutritional quality for consumers such as proteins, carbohydrates, and the retention of contaminants may shed further light on the underlying mechanisms. Our results highlight that aquatic contaminants can affect the physiology of riparian spiders, likely by altering subsidy quality, with potential implications for terrestrial food webs. Environ Toxicol Chem 2023;42:1346-1358. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Historical and current occurrence of microplastics in water and sediment of a Finnish lake affected by WWTP effluents

Only scarce information is available about the abundance of microplastics (MPs) in Nordic lakes. In this study, the occurrence, types, and distribution of MPs were assessed based on the lake water and sediment samples collected from a sub-basin of Lake Saimaa, Finland. The main goal was to estimate the possible effect of the local wastewater treatment plant (WWTP) on the abundance of MPs in different compartments of the recipient lake area. Collected bottom sediment samples were Cs-137 dated and the chronological structure was utilized to relate the concentrations of MPs to their sedimentation years. Raman microspectroscopy was used for the MPs' identification from both sample matrices. In addition, MPs consisting of polyethylene (PE), polypropylene (PP) and polystyrene (PS) were quantified from lake water samples by pyrolysis-gas chromatography-mass spectrometry to provide a complementary assessment of MPs based on two different analysis methods, which provide different metrics of the abundance of microplastics. MPs concentrations were highest in sediment samples closest to the discharge site of WWTP effluents (4400 ± 620 n/kg dw) compared to other sites. However, such a trend was not found in lake water samples (0.7 ± 0.1 n/L). Overall, microplastic fibers were relatively more abundant in sediment (70%) than in water (40%), and the majority of detected microplastic fibers were identified as polyester. This indicates that a part of textile fibers passing the WWTP processes accumulate in the sediment close to the discharge site. In addition, the abundance of MPs was revealed to have increased slightly during the last 30 years.

Plastic debris in plastic-mulched soil-a screening study from western Germany

Background

Agricultural plastic mulches offer great benefits such as higher yields and lower pesticide use. Yet, plastic mulches may disintegrate over time and fragment into smaller debris. Such plastic debris is expected to remain in the field after removal of the plastic mulch and thus contributes to soil contamination with plastics.

Method

To investigate this, we collected soil samples at 0-10 cm and 10-40 cm depth from three fields covered with black mulch film for three consecutive years. Three fields without any reported plastic use served as control. Visual plastic debris > 1 cm (macroplastics) was collected from the soil surface. Mesoplastics between 2 mm and 1 cm were density separated from the sampled soil using saturated NaCl solution and analyzed by Fourier-transform infrared spectroscopy. Debris ≤ 2 mm (microplastics) was dispersed from 50 g soil using sodium hexametaphosphate solution followed by the aforementioned density separation. The separated polyethylene (PE), polypropylene (PP), and polystyrene (PS) were quantified via solvent-based pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS).

Results

With 89-206 fragments ha^-1, the majority of macroplastics were located in fields previously covered with mulch films. 80% of the collected specimen were identified as black PE film. The number of mesoplastics in plastic-mulched soil was 2.3 particles kg^-1, while only 1.0 particles kg^-1 were found in the reference fields. Py-GC/MS revealed microplastic levels of up to 13 mg kg^-1. The PE content was significantly higher in plastic-mulched fields than in reference fields.

Discussion

Although the identified plastic levels are lower than those reported in comparable studies, our results still suggest that plastic mulching functions as a source of plastic debris in agricultural systems. Due to its severely restricted degradability, these plastics are likely to accumulate in soil in the long term and further fragment into smaller and smaller debris.

Validation of a Simple and Reliable Method for the Determination of Aflatoxins in Soil and Food Matrices

Aflatoxins (AFs) are toxic fungal secondary metabolites that are commonly detected in food commodities. Currently, there is a lack of generic methods capable of determining AFs both at postharvest stages in agricultural products and preharvest stages, namely, the agricultural soil. Here, we present a simple and reliable method for quantitative analysis of AFs in soil and food matrices at environmentally relevant concentrations for the first time, using the same extraction procedure and chromatography, either by HPLC-FLD or LC-MS. AFs were extracted from matrices by ultrasonication using an acetonitrile/water mixture (84:16, v + v) without extensive and time-consuming cleanup procedures. Food extracts were defatted with n-hexane. Matrix effects in terms of signal suppression/enhancement (SSE) for HPLC-FLD were within ±20% for all matrices tested. For LC-MS, the SSE values were mostly within ±20% for soil matrices but outside ±20% for all food matrices. The sensitivity of the method allowed quantitative analysis even at trace levels with quantification limits (LOQs) between 0.04 and 0.23 μg kg^-1 for HPLC-FLD and 0.06-0.23 μg kg^-1 for LC-MS. The recoveries ranged from 64 to 92, 74 to 101, and 78 to 103% for fortification levels of 0.5, 5, and 20 μg kg^-1, respectively, with repeatability values of 2-18%. The validation results are in accordance with the quality criteria and limits for mycotoxins set by the European Commission, thus confirming a satisfactory performance of the analytical method. Although reliable analysis is possible with both instruments, the HPLC-FLD method may be more suitable for routine analysis because it does not require consideration of the matrix.

Microplastic Spectral Classification Needs an Open Source Community: Open Specy to the Rescue!

Microplastic pollution research has suffered from inadequate data and tools for spectral (Raman and infrared) classification. Spectral matching tools often are not accurate for microplastics identification and are cost-prohibitive. Lack of accuracy stems from the diversity of microplastic pollutants, which are not represented in spectral libraries. Here, we propose a viable software solution: Open Specy. Open Specy is on the web (www.openspecy.org) and in an R package. Open Specy is free and allows users to view, process, identify, and share their spectra to a community library. Users can upload and process their spectra using smoothing (Savitzky-Golay filter) and polynomial baseline correction techniques (IModPolyFit). The processed spectrum can be downloaded to be used in other applications or identified using an onboard reference library and correlation-based matching criteria. Open Specy's data sharing and session log features ensure reproducible results. Open Specy houses a growing library of reference spectra, which increasingly represents the diversity of microplastics as a contaminant suite. We compared the functionality and accuracy of Open Specy for microplastic identification to commonly used spectral analysis software. We found that Open Specy was the only open source software and the only software with a community library, and Open Specy had comparable accuracy to popular software (OMNIC Picta and KnowItAll). Future developments will enhance spectral identification accuracy as the reference library and functionality grows through community-contributed spectra and community-developed code. Open Specy can also be used for applications beyond microplastic analysis. Open Specy's source code is open source (CC-BY-4.0, attribution only) (https://github.com/wincowgerDEV/OpenSpecy).

Biodegradation and photooxidation of phenolic compounds in soil-A compound-specific stable isotope approach

Phenolic compounds occur in a variety of plants and can be used as model compounds for investigating the fate of organic wastewater, lignin, or soil organic matter in the environment. The aim of this study was to better understand and differentiate mechanisms associated with photo- and biodegradation of tyrosol, vanillin, vanillic acid, and coumaric acid in soil. In a 29 d incubation experiment, soil spiked with these phenolic compounds was either subjected to UV irradiation under sterile conditions or to the native soil microbial community in the dark. Changes in the isotopic composition (δ¹³C) of phenolic compounds were determined by gas chromatography-isotope ratio mass spectrometry and complemented by concentration measurements. Phospholipid-derived fatty acid and ergosterol biomarkers together with soil water repellency measurements provided information on soil microbial and physical properties. Biodegradation followed pseudo-first-order dissipation kinetics, enriched remaining phenolic compounds in ¹³C, and was associated with increased fungal rather than bacterial biomarkers. Growing mycelia rendered the soil slightly water repellent. High sample variation limited the reliable estimation of apparent kinetic isotope effects (AKIEs) to tyrosol. The AKIE of tyrosol biodegradation was 1.007 ± 0.002. Photooxidation kinetics were of pseudo-zero- or first-order with an AKIE of 1.02 ± 0.01 for tyrosol, suggesting a hydroxyl-radical mediated degradation process. Further research needs to address δ¹³C variation among sample replicates potentially originating from heterogeneous reaction spaces in soil. Here, nuclear magnetic resonance or nanoscopic imaging could help to better understand the distribution of organic compounds and their transformation in the soil matrix.

Introducing a soil universal model method (SUMM) and its application for qualitative and quantitative determination of poly(ethylene), poly(styrene), poly(vinyl chloride) and poly(ethylene terephthalate) microplastics in a model soil

Methods for analysis of microplastic in soils are still being developed. In this study, we evaluated the potential of a soil universal model method (SUMM) based on thermogravimetry (TGA) for the identification and quantification of microplastics in standard loamy sand. Blank and spiked soils (with amounts of one of four microplastic types) were analyzed by TGA. For each sample, thermal mass losses (TML) in 10 °C intervals were extracted and used for further analysis. To explain and demonstrate the principles of SUMM, two scenarios were discussed. The first refers to a rare situation in which an uncontaminated blank of investigated soil is available and TML of spiked and blank soils are subtracted. The results showed that the investigated microplastics degraded in characteristic temperature areas and differences between spiked and blank soils were proportional to the microplastics concentrations. The second scenario reflects the more common situation where the blank is not available and needs to be replaced by the previously developed interrelationships representing soil universal models. The models were consequently subtracted from measured TML. Sparse principal component analysis (sPCA) identified 8 of 14 modeled differences between measured TMLs and the universal model as meaningful for microplastics discrimination. Calibrating various microplastics concentrations with the first principal component extracted from sPCA resulted in linear fits and limits of detection in between environmentally relevant microplastics concentrations. Even if such an approach using calculated standards still has limitations, the SUMM shows a certain potential for a fast pre-screening method for analysis of microplastics in soils.

Implications of crop model ensemble size and composition for estimates of adaptation effects and agreement of recommendations

Climate change is expected to severely affect cropping systems and food production in many parts of the world unless local adaptation can ameliorate these impacts. Ensembles of crop simulation models can be useful tools for assessing if proposed adaptation options are capable of achieving target yields, whilst also quantifying the share of uncertainty in the simulated crop impact resulting from the crop models themselves. Although some studies have analysed the influence of ensemble size on model outcomes, the effect of ensemble composition has not yet been properly appraised. Moreover, results and derived recommendations typically rely on averaged ensemble simulation results without accounting sufficiently for the spread of model outcomes. Therefore, we developed an Ensemble Outcome Agreement (EOA) index, which analyses the effect of changes in composition and size of a multi-model ensemble (MME) to evaluate the level of agreement between MME outcomes with respect to a given hypothesis (e.g. that adaptation measures result in positive crop responses). We analysed the recommendations of a previous study performed with an ensemble of 17 crop models and testing 54 adaptation options for rainfed winter wheat (Triticum aestivum L.) at Lleida (NE Spain) under perturbed conditions of temperature, precipitation and atmospheric CO2 concentration. Our results confirmed that most adaptations recommended in the previous study have a positive effect. However, we also showed that some options did not remain recommendable in specific conditions if different ensembles were considered. Using EOA, we were able to identify the adaptation options for which there is high confidence in their effectiveness at enhancing yields, even under severe climate perturbations. These include substituting spring wheat for winter wheat combined with earlier sowing dates and standard or longer duration cultivars, or introducing supplementary irrigation, the latter increasing EOA values in all cases. There is low confidence in recovering yields to baseline levels, although this target could be attained for some adaptation options under moderate climate perturbations. Recommendations derived from such robust results may provide crucial information for stakeholders seeking to implement adaptation measures.

Influence of Organic Chemicals on Water Molecule Bridges in Soil Organic Matter of a Sapric Histosol

Water molecules in soil organic matter (SOM) can form clusters bridging neighboring molecular segments (water molecule bridges, WaMBs). WaMBs are hypothesized to enhance the physical entrapment of organic chemicals and to control the rigidity of the SOM supramolecular structure. However, the understanding of WaMBs dynamics in SOM is still limited. We investigated the relation between WaMBs stability and the physicochemical properties of their environment by treating a sapric histosol with various solvents and organic chemicals. On the basis of predictions from molecular modeling, we hypothesized that the stability of WaMBs, measured by differential scanning calorimetry, increases with the decreasing ability of a chemical to interact with water molecules of the WaMBs. The interaction ability between WaMBs and the chemicals was characterized by linear solvation energy relationships. The WaMBs stability in solvent-treated samples was found to decrease with increasing ability of a solvent to undergo H-donor/acceptor interactions. Spiking with an organic chemical stabilized (naphthalene) or destabilized (phenol) the WaMBs. The WaMBs stability and matrix rigidity were generally reduced strongly and quickly when hydrophilic chemicals entered the soil. The physicochemical aging following this destabilization is slow but leads to successive WaMBs stabilization and matrix stiffening.

Plastic mulching in agriculture. Trading short-term agronomic benefits for long-term soil degradation?

Plastic mulching has become a globally applied agricultural practice for its instant economic benefits such as higher yields, earlier harvests, improved fruit quality and increased water-use efficiency. However, knowledge of the sustainability of plastic mulching remains vague in terms of both an environmental and agronomic perspective. This review critically discusses the current understanding of the environmental impact of plastic mulch use by linking knowledge of agricultural benefits and research on the life cycle of plastic mulches with direct and indirect implications for long-term soil quality and ecosystem services. Adverse effects may arise from plastic additives, enhanced pesticide runoff and plastic residues likely to fragment into microplastics but remaining chemically intact and accumulating in soil where they can successively sorb agrochemicals. The quantification of microplastics in soil remains challenging due to the lack of appropriate analytical techniques. The cost and effort of recovering and recycling used mulching films may offset the aforementioned benefits in the long term. However, comparative and long-term agronomic assessments have not yet been conducted. Furthermore, plastic mulches have the potential to alter soil quality by shifting the edaphic biocoenosis (e.g. towards mycotoxigenic fungi), accelerate C/N metabolism eventually depleting soil organic matter stocks, increase soil water repellency and favour the release of greenhouse gases. A substantial process understanding of the interactions between the soil microclimate, water supply and biological activity under plastic mulches is still lacking but required to estimate potential risks for long-term soil quality. Currently, farmers mostly base their decision to apply plastic mulches rather on expected short-term benefits than on the consideration of long-term consequences. Future interdisciplinary research should therefore gain a deeper understanding of the incentives for farmers and public perception from both a psychological and economic perspective in order to develop new support strategies for the transition into a more environment-friendly food production.