Thank you very much for your time and the rigorous evaluation of our manuscript. We highly appreciate your constructive comments and questions that we believe will help to further improve our work.

In the following, we address all comments point by point and suggest changes for a future manuscript revision (highlighted in bold face).

Method

1. The authors have not included any information on laboratory quality control measures which are a must for microplastics studies. Were laboratory and field blanks analysed and how? What were concentrations in the blank samples? Were deposition blanks conducted during the FTIR analysis? Were samples extracted in a fume hood, were lab coats (what sort) worn during extraction? Were duplicates conducted to assess heterogeneity in the sample? What were your internal standard recoveries, were polymer concentrations recovery corrected? Please include a section for QA/QC in the manuscript.

> Our response: In the submitted version of our manuscript, we intended to keep QA/QC brief and combined it with our method validation (Section 2.6: Method validation and quality control). Therein, we stated that “The soil cores were immediately transferred to uncoated paper bags and air-dried therein to reduce the risk of contamination.” (Lines 83f) and “All measurements were monitored with procedural blanks.” (Line 164).

We will expand this to a more comprehensive QA/QC section which could read as follows:

“To prevent the risk of contamination, all laboratory equipment coming into direct contact with the sample or the extract solution was made of glass, metal, paper, or PTFE. PE, PP, or PS equipment was completely avoided. The worn laboratory coats were of 100% cotton. In addition, all samples and extracts were kept in closed vessels or covered with aluminum foil. The vessels were only opened under a fume hood.

The sample extraction was monitored with weekly procedural blanks that underwent the complete extraction procedure as the samples but without soil addition. Plastic contents in our procedural blanks were exclusively below the LOD.”

Please note that we did not take field blanks because we could hardly treat them in the same way a sampled soil is. But we analyzed all our equipment, including the used paper bags, for their contamination potential and found them not interfering our analysis. In addition, it remains worth noticing that the majority of our soil samples did not contain any plastics (<LOD) which suggests negligible sample contamination.

Furthermore, we did not run FTIR deposition blanks for the particles >2mm since our FTIR–ATR analysis only aimed at the qualitative identification of single suspect particles. In this case, the FTIR signal of the sample surface was expected to significantly exceed that of dust traces on the particle.

Since we designed our study to be a first screening, we ran single measurements only. We suggest to further clarify this in the methods section (Line 136f):

“Each sample was measured once as described in Section 2.3.”

We further did not assess the recovery of our internal standard, namely deuterated PS (PS-d5). This is because PS-d5 was only added after sample extraction and served as a quality control measure for internal instrumental repeatability during measurement sequences.

We suggest to put this more clearly by adding (Line 152f):

“The internal standard PS-d5 was added after sample extraction and used for continuous repeatability checks of sample measurements.”

2. More information is needed on the Py-GC-MS quantification. Why were the dienes chosen for quantification of the polyethylene (PE), was this from a previous published method? Were the samples analysed in full scan or SIM mode?

> Our response: Our solvent-based Py-GC/MS approach was originally published in Steinmetz et al. (2020). In order to avoid extensive repetitions, we tried to keep this short. Yet, we assessed the Py-GC/MS method performance once more in the present manuscript. In Section 3.4, Line 230ff, we stated that “The pyrolysates chosen for PE, PP, and PS quantification were 22:2(1,21), 2,4Me9:1(1), and Sty, respectively, as they performed the best in terms of signal linearity (adj. R2 > 0.995), instrumental LODs (<10 ng), and measurement repeatability (RSD <10 %, Table 2).”.

To make this clearer, we suggest to add:

“The n-alkadiene 22:2(1,21) was preferred over the respective n-alkene or n-alkane because of its higher selectivity for PE (Steinmetz et al., 2020).

Furthermore, our Py-GC/MS measurements were ran in SIM mode, which we report in Line 140ff: “The MS selectively monitored m/zs 70 and 126 for the PP pyrolysate 2,4-dimethyl-1-heptene (2,4Me9:1(1), RI 841), m/zs 104 and 118 for the PS pyrolysates styrene (Sty, RI 895) and α-methylstyrene (αMeSty, RI 981), respectively, and m/zs 82 and 95 for PE n-alkadienes like 1,21-docosadiene (22:2(1,21), RI 2187).”.

To further clarify this, we suggest to add “SIM mode” in parentheses.

3. Styrene is not an ideal pyrolysis product for monitoring polystyrene (PS) as it is not selective. It can originate from organic material (although this may have been removed in your TD analysis) as well as being a pyrolysis product of many other polymers. Typically, the dimer or trimer or polystyrene is monitored. This will increase the MDLs but improve your selectivity. Also, how can you be certain the PS isn’t a sampling/analysis artefact without any blank information? Combined with the poor matrix spike recoveries of PS in the reference soil, your method is not optimised or validated for analysis of PS and you cannot confidently report these results.

> Our response: Our blank chromatograms, these were the weekly procedural blanks (see item 1 above), did not contain styrene at intensities exceeding the LOD; nor did the analyses of our reference soils. In this regard, the selectivity of our method for PS does not originate from choosing styrene as a marker but (1) from the density separation excluding plastics with a density >1.2 g cm^–3 and (2) the subsequent selective dissolution of our target polymers with trichlorobenzene/xylene. We think that this is also the reason why tire wear added to our reference soil at a level twice as high as our highest standard did not induce styrene signals that exceeded the LOD.

Our approach is further in line with Fabbri et al. (2020, doi: 10.1016/j.jaap.2020.104836) who similarly used styrene as a marker compound after polymer dissolution with toluene. The authors argued that dimers may also originate from secondary reactions of monomers with one another, which would challenge their selectivity in general. Such secondary reactions are, however, disfavored when PS is spread on a thin layer or on quartz filters after the solvent has dried. After polymer dissolution, the peak intensities of the PS oligomers are thus considerably lower than those obtained after the pyrolysis of solids. Although this is a very interesting observation, we are reluctant to add it to our discussion (Section 3.4) as it deviates from the common theme of the manuscript and was already addressed by Fabbri et al. (2020). If you and the editor prefer to have this added, we will be happy to do so.

We rather suspect the poor PS recoveries from clay soil to originate from aromatic PS domains interacting with soil particles during the density separation. This is currently discussed in Section 3.4, Line 256ff: “The dramatic decrease in PS recovery may be attributed to interactions forming between the delocalized π-electrons of the aromatic PS ring and SOM, iron and aluminum oxides, or cations bound to the negatively charged surface of clay particles (Newcomb et al., 2017).”.

In line with your suggestion, we should interpret the PS results more carefully. This would include the following additions/modifications in our discussion.

This specifically applies to

Section 3.4 (Line 251):

“Irrespective of the spiking level though, our PS recoveries from the clayey RefeSol 06-A were particularly low (<12 %).”

Section 3.4 (Line 263):

“The 50 % PE and 62 % PP we recovered from RefeSol 06-A suggest a rather semi-quantitative evaluation of soils with a clay content >47 % and a Corg content >2.5 %. PS is evaluated qualitatively for its low recoveries.”

Section 3.5 (Line 286):

“Due to the poor PS recoveries, these findings are most likely underestimated.”

Conclusions (Line 321):

“The combination of soil aggregate dispersion and density separation with solvent-based Py-GC/MS enabled the simple, yet selective quantification of PE and PP debris in agricultural soil. Analyzing a sample amount of 50 g better accounted for the heterogeneous distribution of discrete plastic particles in the soil matrix. The additional dispersion step further made plastic debris occluded in soil aggregates amenable to quantification. By contrast, poor PS recoveries potentially induced by that additional separation step challenged a reliable PS quantification.”

4. Details on PET, PMMA and PVC standards need to be included. What were your tyre wear debris? Were these obtained from a chemical standards company, were they prepared in house and from what type of tyres? Did you really not see a styrene peak from pyrolysis of PVC or from the styrene-butadiene rubber in tyre tread? This suggests your analysis or extraction method is not optimised.

> Our response: We used the same polymers in Steinmetz et al. (2020) and thus refrained from explaining them in detail.

We will add the following explanation to the revised version of our manuscript (Line 162ff):

“The PET came from a cryomilled bottle recyclate (PETKA CZ, Brno, Czech Republic) as detailed in David et al. (2018). The PMMA was ground from a commercial plexiglass provided by Bundesanstalt für Materialforschung und -prüfung (Berlin, Germany). The PVC was purchased from Aldrich Chemistry (Taufkirchen, Germany), and TWD was from a test rig at Bundesanstalt für Straßenwesen (Bergisch Gladbach, Germany).”

As detailed in our response to item 3, our solvent-based Py-GC/MS approach was selective not only because of choosing specific pyrolysis markers but also due to the density separation (1.2 g cm^–3) and selective dissolution with trichlorobenzene and xylene that specifically targeted PE, PP, and PS. PVC and tire wear did not interfere with our analysis because they have a higher density and do not dissolve in the applied extraction mixture.

5. Your samples are filtered at 4 um. Can you comment on possibility of micro/nanoplastics in the smaller size range that may have been missed.

> Our response: Thank you for this important remark. This is a common challenge of current sample preparation methods for the analysis of microplastics in complex matrices. Particles smaller than 4 µm cannot be assessed quantitatively as they will partly flush through the filter but may at a certain stage be retained when the filter becomes increasingly clogged with clay particles. Furthermore, aggregated or coated nanoplastics may be retained more efficiently than virgin ones. Although quite speculative, we would be happy to add these thoughts to our discussion.

At least, we should highlight this drawback in our discussion (Line 248):

“The required filtration step, however, systematically excluded particles <4 µm that were not retained by the used cellulose filter.”

Validation

1. You cannot state your method is validated for plastics in soils when one of your two soil reference materials returned unacceptably low recoveries. Further, your LODs (MDLs) are the concentration where you have acceptable method extraction and analysis recoveries. Considering you have <30% recovery for a 2 ug/g spike in the second reference soil, the method LODs certainly are not 0.3-0.8 ug/g. The extraction method needs further assessment to determine which types of soils are applicable and what the actual MDLs are. I also suggest removing PS from the analysis due to the above mentioned issues.

> Our response: We agree that this needs further clarification. In the current version of our manuscript, we highlighted that the “.. extrapolation of these validity criteria to field samples with a different texture and Corg composition remains difficult and requires careful interpretation.” (Line 249ff). This is a general shortcoming of soil analyses since reference soils will always differ from real soil samples.

For the calculation of LODs, we adhered to the German standard DIN 32645 (2008) and the EURACHEM guideline (Magnusson and Örnemark, 2014) which define the LOD as the minimum amount qualitatively detectable in a blank soil. In this sense, a low recovery close to the LOD (2 µg/g) is not surprising nor contradictory.

We thus suggest to add LOQs to Table 3 and critically discuss this data throughout the manuscript. Note that, according to DIN 32645, the calculation of LOQs is an iterative process that uses the LOD as an initial value but optimizes mostly toward the calibration standards. This is why the LOQs are quite similar in both soils:

Line 233:

“The respective method LOQs ranged from 2.5 to 9.5 mg kg−1 (Table 3).”

Line 237ff:

“Recovering plastic debris at levels close to the method LOD (2 mg kg−1 ) and below the respective method LOQs led to an overestimation of recovered PE (133±9 %) while underestimating PP (70 %) and PS (50 %).”

We further recalculated method LODs directly from the peak intensities of the blank soil. In the first version of our manuscript, we estimated them from averaged soil contents. This now leads to about 1.5 times higher method LODs than before. The slightly elevated LODs reduce the total number of positive detections to 15 which, however, does not affect the outcome of our study.

We suggest to discuss LODs and LOQs in Line 251f:

“Inconsistent recoveries at a spiking level below the method LOQs of 2.5–9.5 mg kg−1 challenged the sensitivity and robustness of our solvent-based approach.”

Line 263f:

“Based on the two reference soils tested and on previous work (Steinmetz et al., 2020), we considered our method sufficiently sensitive and quantitative for environmentally-relevant PE and PP levels exceeding the respective method LOQs. The 50 % PE and 62 % PP we recovered from RefeSol 06-A suggest a rather semi-quantitative evaluation of soils with a clay content >47 % and a Corg content >2.5 %. PS is evaluated qualitatively for its low recoveries.”

We believe that these changes will facilitate the interpretation of our data.

Since the primary aim of our study was to conduct a first screening of agricultural soil, we also limited our reference soils to those of agricultural origin.

2. Line 248 needs to be rewritten, as highlighted above, your method is not sensitive, robust or selective. Similarly, Lines 252-254 needs to be rewritten as I would argue your MDLs are definitely not 1-100 times lower than previously published studies.

> Our response: We agree that we used “robust” in a wrong context since the performance of our method depends on the analyzed soil.

We thus suggest to modify the mentioned lines accordingly and move the text passage to the end of the paragraph (Line 263f):

“Based on the two reference soils tested, we considered our method sufficiently sensitive and quantitative for environmentally-relevant PE and PP levels exceeding the respective method LOQs. The 50 % PE and 62 % PP we recovered from RefeSol 06-A suggest a rather semi-quantitative evaluation of soils with a clay content >47 % and a Corg content >2.5 %. PS is evaluated qualitatively for its low recoveries. These findings once more highlight the importance of specifically testing and evaluating analytical methods for plastic analysis with various soil types (Thomas et al., 2020). The extrapolation of specific validity criteria to field samples with a different texture and Corg composition thus remains difficult and requires careful interpretation.”

Results

1. If you didn’t find any evidence of the plastic covers in the >2mm size fraction, how can you know the PE and PP detected in the <2mm size fraction are from the covers? There is not enough data to make the conclusion that the edge of the sheets are the source of the PE and PS detected on the edges of the field. Are there other common farming sources of the three plastics analysed e.g. tractors/farming equipment? Fertiliser bags? Can these sources be discounted from the study areas?

> Our response: This study aimed at screening commercially managed agricultural fields for plastic debris. With this, we depended on the reports made by the respective farmers. To our knowledge, fertilizer bags were not used. However, we cannot exclude other potential sources. To address this uncertainty, we already discussed that “.. this suggests an external source of plastic debris, for instance from adjacent streets or other fields, or residues from previous land use (Harms et al., 2021).” (Line 226ff). In Line 301, we further reason: “Even at larger scales though, it remained unresolved to what extent the PE debris in the field periphery (mainly sites 7 and 8) originated from the covered field centers or whether it came from an external source via wind drift. Due to ubiquity of products made from PE, such an external source cannot be excluded.”

Yet, we will communicate the uncertainty of our results in a clearer way in the revised version of our manuscript. We suggest the following amendment (Line 312f):

“In the past, beads made from expanded PS were used for the conditioning and stabilization of horticultural soils (Maghchiche et al., 2010). However, it remained unresolved whether this was the case for the agricultural field investigated in this study.”

2. I would suggest the low detection and variable PS results are due to the extraction method not performing for clay type soils (which are most of the sites). Did the soil type differ between the field and the periphery where the PS was detected? Again, it would be good to have field blank information here and confirmation from another PS pyrolysis product.

> Our response: The screened soils have a clay content of 15–36 % which ranges between that the two reference soils (8 and 47 % clay). For that reason, we expected that the method will perform within this range. Please see also our response further above addressing PS pyrolysis products and blanks.

We suggest to add the following to

Section 3.4, Line 270:

“The 50 % PE and 62 % PP we recovered from RefeSol 06-A suggest a rather semi-quantitative evaluation of soils with a clay content >47 % and a Corg content >2.5 %. PS is evaluated qualitatively for its low recoveries.”

Section 3.5, Line 314:

“Given that our investigated soils had a clay content of 15–36%, the obtained PE, PP, and PS contents were potentially underestimated by a factor of 1.5–2.”

3. There is not enough data to state that PE detected at sites 1,7,8 are from the perforated foils and there is not enough data to make the conclusion that application of a foil for 4 months results in detectible PE microplastics in the soil (Line 289).

> Our response: We agree that we should more clearly address the uncertainty of our results. We suggest the following additon to Line 291:

“On the one hand, this is remarkable because the agricultural films were on site for four months only. On the other hand, the elevated plastic contents may have originated from another, potentially diffuse input source prior to plastic coverage.”

Conclusions

1. The method is not robust, as it does not have high recoveries for different soil types. Also, the method is not successfully validated as described above.

> Our response: We used “robust” in the wrong context here and suggest to remove it from this sentence. In a future revised version, it would read:

“The combination of soil aggregate dispersion and density separation with solvent-based Py-GC/MS enabled the simple, yet selective quantification of PE and PP debris in agricultural soil. Analyzing a sample amount of 50 g better accounted for the heterogeneous distribution of discrete plastic particles in the soil matrix. The additional dispersion step further made plastic debris occluded in soil aggregates amenable to quantification. By contrast, poor PS recoveries potentially induced by that additional separation step challenged a reliable PS quantification.”

2. As discussed above I disagree with the statement that 4 months of covering with thinner perforated foils is associated with elevated PE content as there is no evidence that the PE originated from the foil and not other sources.

> Our response: We would like to emphasized that this linkage does not indicate a causal relationship. To clarify this, we suggest the following addition:

“Due to the ubiquitous use of plastic covers and potentially interfering external plastic sources, a causal relationship between the use of plastic covers and elevated plastic levels in soil needs yet to be shown, for instance, by conducting more controlled and systematic experiments.”

Specific comments

Line 90: thermodesorption should be thermal desorption

> Our response: Thank you for this remark. We will correct this throughout the manuscript

Line 113: How were the soil cores homogenised?

> Our response: The soil cores were sieved as a whole and homogenized manually directly after. We suggest to add this information as follows (Line 113):

“All soil cores were sieved to fine soil (≤2 mm) and homogenized manually as suggested by Thomas et al. (2020).”

Line 199: Please expand BHT and please include the spectral matches as a Figure for all the NIST library identified compounds from the TD analysis.

> Our response: We wrote out BHT throughout the manuscript. We further suggest to add the following figure for the comparison of spectral matches to the appendix:

Line 200: Do you have any reference for propyl dodecanoate and oleonitrile being added to agricultural plastic covers?

> Our response: The cited reference (Hahladakis et al., 2018) only provides general information on common polymer additives. Polymer additives of specific commercial products like agricultural covers are typically a trade secret and have to our knowledge not been published yet. If you have more detailed insights, we would be happy to have your support.

Line 206: The lower melting temperatures of PP covers (than virgin PP) may indicate addition of additives or impurities to the PP covers.

> Our response: This is interesting. We will modify the following sentence (Line 208) accordingly:

“Decreasing melting temperatures may indicate the presence of additives or other impurities but could also be a first sign of polymer aging as similarly observed after 5–20 months of temperate weathering (Tocháček et al., 2019)”

Line 310: Have these PS beads been used in Germany? Do you know if they were applied to these sites?

> Our response: We do not know for sure. This is why we discuss different possibilities here.

Line 315: What size range did the previous studies use and how do they compare to your study (4um-2mm).

> Our response: Solvent-based Py-GC/MS methods are still a new and emerging field. To our knowledge, other solvent-based approaches have not yet been combined with density separation. While density separation allows for higher sample amounts to be analyzed (50 g), it requires subsequent filtration which may systematically exclude smaller particles. Dierkes et al. (2019) directly extracted 1 g of soil with ASE. The soil was not sieved and no lower size cutoff was reported for the used ASE filters/membranes. Primpke et al. (2020) used filters with a pore size of 1 µm for the quantification of microplastics in sediment and water. The authors, however, directly analyzed the crushed filters without dissolving the polymers. For these reasons, detailed comparisons are difficult to draw at the current stage.

Figure A1: Please overlay the reference spectra with the samples for comparison

> Our response: We modified the Figure A1 as suggested:

We further applied the same modifications to Figure A3 (now A4):

Thank you very much for your time and the thorough evaluation of our manuscript. We highly value your constructive comments and questions that we believe will help to further improve our work.

In the following, we address all comments point by point and suggest changes for a future manuscript revision (highlighted in bold face).

General

Very welcome is the point, that the authors says, that this is a „first screening“ and not a final result (including a worldwide calculation) for the rest of the world. Therefore I would avoid the deeper comparison to other studies (especially to Dierkes 2019), especially when other techniques were used. Ever through these authors did not interpret their work as a „snapshot“, the goal of this article should be this „first screening“. Furthermore the study should focus on the results and not on the comparison of the methods (Who is the best one?). Therefore, please shortens the text between L. 263-274, nobody needs this „Hunt for the lowest LOD“ any more.

> Our response: Thank you for this remark. Following your recommendation, we suggest to substantially shorten the paragraph to:

“While this clearly defines the quantitative limits of the method, our working range is still 10–100 times lower than that of previous applications involving solvent-based Py-GC/MS. Dierkes et al. (2019) and Okoffo et al. (2020), for instance, spiked 1 g of quartz sand and biosolids at 0.05–50 g kg−1 of various polymers to evaluate their accelerated solvent extraction with THF and DCM, respectively.”

Specific comments

Is there an meaningful reason for separation of particles larger than 2 mm and subsequent analysis using ATR-FTIR or should it be better to go down with the limit value to 0,5 mm for example?

> Our response: Our solvent-based Py-GC/MS method was intended as a first and simple screening tool for soil-associated plastic debris that complies with the definition of fine soil (<2 mm). FTIR–ATR was used as a complement for all remaining larger particles.

The advantage of the present method (density separation, polymer extraction and detection) in comparison to the method of Dierkes (polymer extraction and detection) is the investigation of a higher field sample volume. Therefore it is expected, to get a more homogeneous, representative result. Did the authors proved this by various loading of sample volume with spiked polymers? Otherwise, please comment this more clearly and highlight this as a advantage from the beginning (not in the conclusion!)

> Our response: We did not assess various sample amount for sample homogeneity but simply aimed for a maximum sample size from the beginning on. To acknowledge this, we suggest to move this to the introduction instead of a results (Line 48ff):

“To better account for the heterogeneous distribution of plastic debris in soil, we further refined and validated a new sample preparation procedure involving soil aggregate dispersion and density separation that allowed for the analysis of up to 50 g soil.”

L.84: Please check, if paper bags contain PS signals. PS copolymers are often used for paper stabilisation and might be a source for the unclear PS signals. The reason in L 314 is very speculative and should be deleted, so far this is not documented for the investigated soil.

> Our response: Thank you for this important remark. We measured the paper bags with our solvent-based method. An extract with 250 µg/mL paper in trichlorobenzene/xylene, which exceeded the maximum concentration of our calibration curve, did not induce any PS or PE and PP signals above LOD. We agree that Lines 310–313 are rather speculative. However, such information may be a good starting point for other researchers to conduct a follow-up study on this issue. We suggest to modify the sentence in Line 312 to better communicate the underlying uncertainty of our statement:

“In the past, beads made from expanded PS were used for the conditioning and stabilization of horticultural soils (Maghchiche et al., 2010). However, it remained unresolved whether this was the case for the agricultural field investigated in this study.”

L.104-110: No data from MS of TGA/MS are presented. Therefore please delete this as an information (just TGA).

> Our response: We changed TGA/MS for TGA throughout the manuscript and suggest to modify Lines 104–109 as follows:

“DSC and TGA measurements were conducted in accordance with David et al. (2018). In brief, DSC was applied between −50 and 250 °C (10 K min−1 ramp, 50 mL min−1 N2 flow, Q1000, TA Instruments, New Castle, US) to determine the melting and crystallization temperatures of the agricultural plastic films. For the determination of polymer degradation onsets, plastic samples were subjected to TGA (STA 449 F3 Jupiter, Netzsch, Selb, Germany). The heating ramp was 5 K min−1 from 40 to 1000 °C under a 20 mL min−1 Ar flow. The degradation onset was determined by the temperature at which the polymer starts to thermally decompose (<1 % mass loss).”

L.160-162: No results from measurements using PET, PMMA, PVC, TWD are given. Please delete this information.

> Our response: PET, PMMA, PVC, and TWD were used to assess whether particularly high contents of those four polymers interfere with the selective quantification of our target polymers PE, PP, and PS. The results are reported in Line 234f and Table 3 (Interference). We suggest to rephrase this sentence to make the main message clearer:

“A LUFA 2.2 soil containing each 40 µg g−1 of potentially interfering, non-target PET, PMMA, PVC, and TWD did not induce significant false positive detections of PE, PP, or PS.”

L.184: Thermoanalysis include DSC, TGA and also others methods (DMA, Rheology etc.). In this present meaning it is related to DSC. Make this more precise, to avoid misunderstanding.

> Our response: Corrected:

“Complementary DSC analysis showed crystallization temperatures at 114–116 °C and melting temperatures at 158–160 °C. Between 381 and 400 °C, the polymers started to decompose into methylalkenes characteristic for PP (Tsuge et al., 2011, Fig. A2a for an exemplary pyrogram).”

L.185, 193: Please define what the meaning of degradation onset’s means. Include the determination of this value.

> Our response: We suggest the following explanation:

“The degradation onset was determined by the temperature at which the polymer starts to thermally decompose (<1 % mass loss).”

L.199, 212: BHT is not a common additive for polymers. It is as a antioxidant to small and tends to migrate from the polymer bulk. The observed signal is probably related to the thermal decomposition product (or because of degradation process) of Irgafos 168 or Irganox 1010, etc.

> Our response: Thank you for this important remark. We implemented your suggestion as follows:

“In addition, the PP fleeces from sites 1 and 2 as well as the PE perforated foils from sites 4–8 contained traces of a di-tert-butylphenol (for instance CAS 96-79-4) which is an indicator for antioxidants (Hahladakis et al., 2018).”

L.199: please replace slip agent by lubricant, is more common.

> Our response: Corrected.

L.201-202: The Non-identification of pesticides are very surprisingly: Are they used during the period of agriculture? Or are they expected as a additive in the plastic materials?

> Our response: To our knowledge, the investigated covers were not marketed with added pesticides. However, it is common practice to continue pesticide applications while the agricultural covers are in place. For that reason, we also wondered why we did not find traces of those pesticides on the covers. As we discuss in Line 201f this was “.. probably due to the limited sensitivity of the qualitative analysis and/or their low thermal stability.”. Yet, the screening of pesticides was not the primary goal of our study but we found this an interesting side note worth sharing with the scientific community.

L. 215pp: please comment the very intensive signals about 1000 cm-1 in the ATR-FTIR spectra, which are not related to PE or PP.

> Our response: We added the following sentences for clarification:

“The indistinct band between 1200 and 900 cm−1 may be attributed to C−O stretching in alcohols, acids, or ethers originating from a contamination with SOM or plastic aging (Fu et al., 2021).”

Used literature:

Fu, Q., Tan, X., Ye, S., Ma, L., Gu, Y., Zhang, P., Chen, Q., Yang, Y., and Tang, Y.: Mechanism Analysis of Heavy Metal Lead Captured by Natural-Aged Microplastics, Chemosphere, 270, 128 624, https://doi.org/10.1016/j.chemosphere.2020.128624, 2021.

L.230pp: The low recovery rate of PS is surprisingly, because PS is the best soluble polymer compared to PE and PP. The explanation in l. 257 is very speculative and needs a approval. I expect, that part of the PS degrades to smaller PS oligomers or monomers, which does not fit to the calibration signals of reference measurements. PS is very sensitive to depolymerisation (Ceiling Temperature!), therefore I expect a significant lost of signals due to degradation during density separation and extraction processes.

> Our response: In our previous study (Steinmetz et al., 2020), we applied a similar solvent-based Py-GC/MS approach on the same reference soils but without prior density separation. We obtained PS recoveries ranging from 77 to 119 %. Given that we also dissolved our PS standards prior to Py-GC/MS analysis, we assumed the additional density separation to be the driving factor for the low PS recovery. However, we used saturated NaCl solution for density separation which we expected to have a negligible influence on PS depolymerization. From our perspective, this leaves polymer–mineral interactions as the most likely explanation which is also in line with the discussed literature.

L.275pp: Are all measurements using PY-GC/MS realised only once, or are there repetitive measurements at single samples?

> Our response: Since we designed our study to be a first screening, we ran single measurements only. We suggest to further clarify this in the methods section (Line 136f):

“Each sample was measured once as described in Section 2.3.”