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，通过种植实践应用到产品包装的整个农业供应链中。地膜就是这样一种‘塑料栽培’应用，即在土壤表面铺展不透明的薄膜，以形成保护屏障，并在作物/水果土壤-根区保持湿润的小气候。地膜是农业生态系统的人为化学输入来源，其生态毒理遗产尚待评估。制造商在塑料配方中加入了多种化学添加剂，以帮助制造、改善功能性、延缓降解并改变美学。在大多数情况下，添加剂不是在化学上而是物理上与聚合物基质结合，这意味着随着时间的推移，它们可以自由释放到周围的农业生态系统。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，具体涉及环境化学。该项目的第一个目标是开发用于低密度聚乙烯(LDPE)和可生物降解产品聚乳酸/聚己二酸对苯二甲酸丁二醇酯(PBAT)地膜的化学表征方法。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，将化学添加剂含量从聚合物体系中分离出来。然后使用气相色谱(GC)和质谱仪(MS)技术对化学提取物进行筛选，以鉴定和定量添加剂和非故意添加物质(NASS)。为了补充这些发现，还开发了表征地膜聚合物组成的方法。其中包括参照聚合物标准的傅里叶变换红外光谱分析和核磁共振光谱分析。有了塑料化学成分的知识，通过有针对性的化学筛选方法，就可以评估向土壤等农业生态系统隔间释放的化学物质。第二个目标是评估地膜中具有特征的化学成分的短期淋溶行为。为此，将塑料薄膜在水中孵化28天，并使用GC-MS和GC-火焰电离检测器(FID)对渗滤液中的塑料衍生化学物质进行筛选。然后，在现场使用期间，特征化合物被确定为从塑料中短期内流动性最强的化合物。第三个目标集中在模拟农业生态系统隔间内任何释放的化学品的寿命。这一点对于评估地膜在生长季节后可能保留在土壤中尤其重要，这意味着随着时间的推移，化学成分将释放到更广泛的环境中。为了评估化学持久性，目标添加剂被加入到土柱中，并在56天内定期采样。开发了一种超声波辅助溶剂提取程序，随后进行了有针对性的化学表征，使土壤基质中的化学稳定性得以暂时评估。培养是在混合添加剂体系中进行的，也是针对单个分析物进行的。这使得可以确定某些塑料添加剂比其他塑料添加剂更优先降解，并评估添加剂的稳定性是否因混合化学物质暴露而改变。

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.