Plant residues are the main source of organic matter in soil; this process takes place naturally in forests and with organic amendments in farmlands. Terrestrial plants also synthesize hydrocarbons. Typically, angiosperms contain hundreds to thousands of milligrams of long chain n-alkanes per kilogram in leaf waxes. However, petroleum pollution is a worldwide issue, and different national regulations set the guideline limit for petroleum hydrocarbons in green areas at 50 mg kg^–1. Focusing on the Italian legislation as a case study, we hypothesized that direct or indirect high inputs of plant residues could lead the level in the soil to exceed this limit, resulting in a false positive petroleum contamination. Therefore, we investigated the occurrence of hydrocarbons in soils with different inputs of natural or farming biomasses. The highest total petroleum hydrocarbon (TPH) concentrations were found in background soils from protected woodlands, remarkably with most samples resulting in levels above the guideline limit. Similarly, the TPH concentrations in agricultural soils amended with compost and digestate were higher than those in samples of soil in which only chemical fertilizers were used. n-Alkane carbon preference indices underlined the role of plant residues as a source of hydrocarbons in these samples, clearly distinguishing spiked petrogenic contamination. Possible revisions of the regulatory and analytical methods are then discussed.

中文翻译：

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植物残渣作为土壤中碳氢化合物的直接和间接来源：当前的问题和法律含义

植物残渣是土壤中有机物的主要来源。这个过程自然发生在森林中，在农田中进行有机改良。陆地植物也合成碳氢化合物。通常，被子植物每公斤蜡中含有数百至数千毫克的长链正构烷烃。但是，石油污染是一个世界性的问题，不同的国家法规将绿色区域中的石油碳氢化合物的准则限值设定为50 mg kg ^–1。我们以意大利的立法为例进行研究，我们假设直接或间接地大量输入植物残渣可能导致土壤中的水平超过该限值，从而导致假阳性石油污染。因此，我们调查了天然或农业生物质输入不同的土壤中碳氢化合物的发生情况。在受保护的林地的背景土壤中发现最高的总石油烃（TPH）浓度，其中大多数样品的含量最高都超出了指导限值。同样，用堆肥和消化液改良的农业土壤中的TPH浓度也比仅使用化肥的土壤样品中的TPH浓度高。ñ-烷烃碳偏好指数突显了这些样品中植物残留物作为碳氢化合物来源的作用，从而清楚地区分了加标的成岩污染。然后讨论了监管和分析方法的可能修订。