Aging rate, environmental risk and production efficiency of the low-density polyethylene (LDPE) films with contrasting thickness in irrigated region.

Physical thickness of low-density polyethylene (LDPE) films might determine the release rate of phthalic acid esters (PAEs) & structural integrity and affect production efficiency. However, this critical issue is still unclear and little reported. Aging effects were evaluated in LDPE films with the thickness of 0.006, 0.008, 0.010 and 0.015 mm in a maize field of irrigation region. The Scanning electron microscope (SEM) results showed that the proportion of damaged area (Dam) to total area of LDPE films was massively lowered with increasing thickness after aging. The highest and lowest Dam was 32.2% and 3.5% in 0.006 and 0.015 mm films respectively. Also, the variations in peak intensity of asymmetric & symmetrical stretching vibrations (ASVI & SSVI) were detected using Fourier transform infrared spectrum (FTIR), indicating that the declines in peak intensity tended to be slower with thickness. Interestingly, the declines in physical integrity were tightly associated with increasing exhalation rate of PAEs. Average releasing rate of PAEs was 38.2%, 31.4%, 31.5% and 19.7% in LDPE films from 0.006 to 0.015 mm respectively. Critically, thicker film mulching can lead to greater soil water storage at plough layer (SWS-PL) and better thermal status, accordingly harvesting higher economic benefit. Therefore, LDPE film thickening may be a solution to reduce environmental risk but improve production efficiency in arid region.

Fate of plastic film residues in agro-ecosystem and its effects on aggregate-associated soil carbon and nitrogen stocks.

Biodegradable (Bio) plastic films are widely viewed as promising alternative products of low-density polyethylene (LDPE) films to minimize plastic debris accumulation and pollution in agroecosystems. Yet, this speculation indeed lacks of sufficient evidences. We conducted a landfill investigation on the aging characteristics of Bio and LDPE plastic films in maize field, and the effects on soil aggregate composition and carbon & nitrogen stocks. The degradation rate of Bio film was up to 41.1% while that of LDPE film was zero. Scanning electron microscope (SEM) showed that the crack formation of Bio film had a pronounced domino effect, and FTIR showed that old Bio film displayed an extra wide peak threshold ranging from 3000 to 3500 cm-1. Particularly, the abundance of microplastics was elevated with the increased plastic residues, and the increment mostly resulted from Bio residues. Critically, plastic residues significantly lowered the soil macro-aggregates (>0.25 mm) proportion, while increasing that of micro-aggregates (0.1-0.25 mm) in LDPE, and silt/clay fraction (<0.1 mm) in Bio respectively. They significantly promoted total nitrogen content of the aggregates with the same size, but decreased the organic carbon content, dramatically lowering the C/N. Therefore, we first identified the fate of plastic film residues in agroecosystems and revealed the serious deficiencies of Bio plastic film.