and mitigate heavy metal

Overview

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Key numbers

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antimicrobial agents5,12, with a demand of about 5% of the weight of plastic products13. Besides, toxic metals such
from 0.10 to 2.40 €/kg, encompassing both conventional and eco-labeled substrates (Table S2 and Fig. S1).
All isolated microparticles were analyzed by means of a Thermo Nicolet 5700 Fourier transformed infrared
in the range of 400–4000 cm−1. Spectra were controlled and evaluated by the OMNIC software without further
Compounding Materials (350 spectra). A hit quality percentage match > 60% was used as the threshold for
performed with a Crison GLP22 pH-meter, calibrated by means of standard solutions, and the elemental analysis
regia), after a final extract volume of 50 mL with ultrapure water (Type I) (See Table S3 in Supplementary
(H0) to compare paired data and identify statistically significant differences. The interquartile range (IQR) was
using Pearson’s correlation coefficient (r). All statistical analyses were considered statistically significant at a 95%
Microparticles selected and identified using ATR-FTIR resulted in 59.06% MPs, 26.17% as non-plastic particles,
such as bentonite or silk, and 14.77% as unidentified particles. MPs were observed in all compost products, with
the range reported by Weithmann et al.23 in organic fertilizer converted from biosolid (14–895 items/kgdw) and
through a composting process (CB5, 73.62 ± 2.43 items/kgdw) (see Table S4 for post-hoc analysis). In fact, the
In terms of concentration, the calculated average value of MPs in compost samples was 67.89 ± 13.09 mg/kgdw
(IQR 57.85 mg/kgdw), with a maximum value of 631.14 mg/kgdw corresponding to CB9. Bläsing and Amelung29
reported an abundance of 2.38–180 mg/kg of plastic fragments > 0.5 mm in organic fertilizer. Our commercial
universal substrate CB3 contained the highest average microplastic concentration (269.03 ± 112.99 mg/kgdw),
followed by blonde peat compost (CB9) (178.42 ± 151.63 mg/kgdw), almost twice as high as the third average
microplastic concentration (CB1: 77.41 ± 20.41 mg/kgdw). The lowest one (10.86 ± 2.67 mg/kgdw) was found in
significant lower microplastic concentration (26.45 ± 15.23 mg/kgdw) than non-eco ones (85.56 ± 17.07 mg/kgdw)
with a size > 1 mm accounted for more than 60% of the total MPs, being between 1 and 2 mm the most common
size (42.50%) (Fig. 2a) (see Table S5 for post-hoc analysis).
The MPs shape varied among different brands, with average percentage values of 36.36% for films, 26.14%
of film was higher for commercial universal substrate composts (36.36%) than for the other ones (26.63%). As
Different letters mean significant differences (p < 0.05).
depicts distinctive absorption peak band examples for six identified polymers, and Table S6 (Suppl. Inf.) collects
The most abundant polymers were AG and CEL, especially in non-eco products (25% and 12.5%, respectively),
compared to eco composts (2.27% and 10.23%, respectively). The occurrence of chipboard or agglomerate polymer
disposal of furniture waste, construction debris, or laminated packaging. Therefore, 83.33% of this polymer
was isolated in commercial universal substrates, while other polymers such as CEL (55%), CP (50%) or ACR
(50%) were unevenly distributed throughout all the compost products. Together with PE, these five polymers
accounted for 77.27% of the plastic material found in compost samples. CP is widely used in food packaging
being reported as the most common MPs in Chinese table salts from lakes, rocks, and wells36 and in the marine
The main physicochemical parameters of compost products are shown in Table 1. A statistically significant
the compost (r = − 0.482, p = 0.000). The average percentage of nitrogen proved to decrease from 1.54 ± 0.07%
acrylate (ACR) (match: 70.80%), (b) CB5: polyethylene (PE) (match: 83.70%), (c) CB8: polypropylene-
terephthalate (PET) (match: 81.30%), (f) CB8: polypropylene (PP) (match: 92.96%).
Table 1. Physicochemical parameters of the compost products. IC, Inorganic carbon; TOC, Total organic
The percentage of nitrogen was statistically higher by 26% in vermicompost (CB4) compared to the rest of the
than 400%) could be caused by the accumulation of Ca into the Eisenia fetida tissue55.
The composition of trace elements is shown in Table 2. Statistically significant inverse bivariate correlations
depicted in Table 1, with a maximum of 10 for CB1 and a minimum value of 1 for CB11. A statistically significant

Methods (brief)

samples, with an average abundance of 137.65 ± 6.01 items/kgdw, and concentrations up to 631.14 mg/
0.60 €/kg); (CB11) Eco-substrate for cactus (price: 1.52 €/kg). Compost samples were selected to represent a
Fertilizer samples were first sieved through a 5 mm stainless steel screen to remove coarse particles that could
achieved, in a forced air stove FD 23, to ensure consistent moisture removal across all samples. After that,
three independent replicates of each of the eleven compost samples were processed by centrifugation, which
samples were centrifuged in a Z-383 K centrifuge, using a fixed-angle rotor in glass centrifuge tubes (15 mL)
NaCl extraction process was repeated twice, and total supernatants for each sample on petri dishes were placed
spectra collected by attenuated total reflectance (ATR) were an average of 20 scans with a resolution of 16 cm−1
Compost samples were also analyzed for eighteen trace elements that are proxies for important additives in
microwave oven digestion procedure was carried out by an UltraWAVE ECR Microwave Digestion System (Fig.
digestion vessel, with 3 mL of concentrated HNO3 (69%) and 1 mL of concentrated HCl (37%) (reverse aqua
Digested samples were then filtered and 1:5 dilutions were made prior to the analysis of trace element
content using inductively coupled plasma mass spectrometry (ICP-MS) (Fig. S7). The ICP-MS was equipped
identified in each compost sample, excluding cellulosic-based microplastics (i.e., cellulose, cellophane). Formally,
where Pi = 1 if the ith petroleum-based polymer type is present in the sample, and Pi = 0 otherwise, and n is the
also acting as negative control samples or procedural blanks. Eleven 60-mm glass Petri dishes were kept open
during all analytical processes, one for each compost sample, as well as two solvent blanks of NaCl solution
120 g/L (ρ = 1.08 g/cm3), that were analyzed throughout the entire study. MPs identified in control samples were

Implications

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Update history

The five most recent substantive edits to this page, classified major (evidence or structure moved), correction (a published value or statement was wrong and has been fixed), or minor (narrative rewritten without changing the underlying evidence). Each description is derived from what the edit did to this page; the linked commit is the authoritative record, routine regeneration passes are excluded, and the full version history lives in git. When DOI minting comes online (see schema docs), each entry below will also link to a version-pinned DataCite DOI.

Commit	Date	Change	Description
b01ec52c	2026-08-04	major	2 sections added
d49e450f	2026-08-03	major	5 sections added; narrative text revised