Chemical Characterisation of Agricultural Plastic Mulch Film and Assessment of Anthropogenic Chemical Release to Agroecosystem Compartments

塑料是一种重要的材料，应用于整个农业供应链，从种植实践到产品包装。地膜就是这样一种“塑料栽培”应用，其中不透明的薄膜在土壤表面上伸展，形成保护屏障，并在作物/水果土壤-根部区域保持潮湿的小气候。地膜是农业生态系统的一种人为化学输入源，其生态毒理学遗产尚待评估。制造商在塑料配方中加入了多种化学添加剂，以帮助制造，改善功能，延缓降解和改变美观。在大多数情况下，添加剂不是化学地而是物理地结合到聚合物基质上，这意味着随着时间的推移，它们可以自由地释放到周围的农业生态系统中。为了追踪化学添加剂在生态系统中的释放程度和随后的相互作用，必须首先确定薄膜的配方。该项目属于EPSRC的物理科学主题，特别是与环境化学有关的福尔斯。该项目的第一个目标是开发农用塑料地膜的化学表征方法，用于低密度聚乙烯（LDPE）和生物降解制品聚乳酸（PLA）/聚己二酸丁二醇酯对苯二甲酸酯（PBAT）地膜。开发的方法包括使用基于溶剂的提取技术，如微波辅助提取（MAE）和溶解沉淀提取，以从聚合物系统中分离化学添加剂的内容。然后使用气相色谱（GC）和质谱（MS）技术筛选化学浸提液，以识别和定量添加剂和非故意添加物质（NIAS）。为了补充这些发现，还开发了覆盖膜的聚合物组合物的方法。这些包括傅立叶变换红外（FTIR）光谱和核磁共振（NMR）光谱与聚合物标准的分析。随着对塑料化学成分的了解，通过有针对性的化学品筛选方法，评估化学品释放到农业生态系统分区（如土壤）的情况变得可行。第二个目的是评估短期浸出行为的特征化学成分从地膜。为此，将塑料覆盖物在水中孵育28天，并使用GC-MS和GC-火焰离子化检测器（FID）筛选沥滤液中的塑料衍生化学品。然后将表征的化合物鉴定为在现场使用期间短期内从塑料中最移动的。第三个目标侧重于模拟农业生态系统隔间内任何释放的化学品的寿命。这对于评估给定的地膜在生长季节后可能保留在土壤中特别重要，这意味着化学成分将随着时间的推移释放到更广泛的环境中。为了评估化学品持久性，将目标添加剂掺入土壤柱中，并在56天内定期取样。一个发达的超声辅助溶剂提取程序，然后有针对性的化学表征，允许土壤基质内的化学稳定性进行暂时评价。在混合添加剂系统和单个分析物中进行孵育。这允许识别某些塑料添加剂相对于其他添加剂的优先降解，并评估添加剂稳定性是否因混合化学品暴露而改变。

Plastic is a prominent material applied throughout agricultural supply chains through cultivational practices to product packaging. Mulch film is one such 'plasticulture' application where opaque film is stretched over the soil surface to form a protective barrier and maintain a humid microclimate in the crop / fruit soil-root zone. Mulch film represents an anthropogenic chemical input source to agroecosystems, whose ecotoxicological legacy is yet to be assessed. Manufacturers include a diverse multitude of chemical additives in plastic formulations to aid with manufacturing, improve functionality, retard degradation and alter aesthetics. In most cases, additives are not chemically but physically bound to the polymeric matrix meaning over time they are free to be released to the surrounding agroecosystem. To trace the extent of release and subsequent interaction of chemical additives within ecosystems, the formulation of the film must first be determined. This project falls within the physical sciences theme of the EPSRC, specifically relating to environmental chemistry. This projects first aim was to develop methods for the chemical characterisation of agricultural plastic mulch film, for both low density polyethylene (LDPE) and biodegradable articles polylactic acid (PLA)/polybutylene adipate terephthalate (PBAT) mulch film. Developed methods included the use of solvent-based extraction techniques, such as microwave assisted extraction (MAE) and dissolution-precipitation extractions, to separate the chemical additive content from the polymer system. The chemical extracts were then screened using gas chromatography (GC) and mass spectrometry (MS) techniques for the identification and quantification of additives and non-intentionally added substances (NIASs). To compliment these findings, methods to characterise the polymeric composition of the mulch film were also developed. These included analyses with fourier transform infrared (FTIR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy with reference to polymer standards. With attained knowledge of the plastics chemical composition, assessment of chemical release to agroecosystem compartments, such as soils, became feasible through a targeted approach of chemical screening. The second aim was to assess the short-term leaching behaviour of the characterised chemical constituents from mulch film. For this, plastic mulch was incubated in water for 28 days and the leachate was screened for plastic derived chemicals using GC-MS and GC-flame ionisation detector (FID). Characterised compounds were then identified as the most mobile from the plastic in the short term, during in field use. The third aim focussed on the lifetime of any released chemicals within a simulated agroecosystem compartment. This was especially important to evaluate given mulch film may be retained in the soil after a growing season, meaning the chemical content will over time be released to the wider environment. To assess chemical persistence, target additives were incorporated into soil columns and periodically sampled over a 56-day period. A developed sonication assisted solvent extraction procedure, followed by targeted chemical characterisation, allowed the chemical stability within the soil matrix to be temporally evaluated. The incubations were undertaken in both a mixed additive system and for individual analytes. This allowed for the identification of preferential degradation of certain plastic additives over others and to evaluate if additive stability is altered by mixed chemical exposure.