Iticescu et al. 2021 — Heavy metals in Galati sewage sludge for Romanian agricultural use

A characterisation study of municipal sewage sludge from the Galati Wastewater Treatment Station (south-east Romania) intended for application as an agricultural soil amendment, sampled quarterly across 2017–2018 in eight sets (four undigested, four post-anaerobic-digestion). The authors monitored sludge pH, nutrients, and the three heavy metals required by national rules for agricultural reuse (Cr, Cu, Ni), and characterised the two soil types receiving the sludge before and after calcareous amendment. Reported metal concentrations in sludge and in receiving soils are well below the Romanian and EU regulatory ceilings for agricultural land application; the authors attribute this to the loss of heavy industry from the Galati municipal catchment after 1990.

Key numbers

Reported values are read from the published figures and tables; the article does not include a numerical table of per-set heavy metal concentrations (Figure 3, p. 6) and the authors only summarise the soil dispersion through a county map (Figure 5, p. 8) rather than a numerical table.

Sludge characterisation

• Quarterly sample sets n=8: Feb–Mar 2017; Sep–Oct 2017; Feb–Mar 2018; Aug–Sep 2018; sets 1–4 undigested, sets 5–8 anaerobically digested (p. 3).
• WWTS Galati produces approximately 3,200 t sludge per year (p. 3).
• Sludge pH range across the eight sets: 7.76–8.85 upH (p. 6).
• Heavy metal content in sludge (mg·kg⁻¹ dry substance, Figure 3 bar chart, qualitative read):
  • Ni: range across sets approximately 1.10–2.00 mg·kg⁻¹ d.s.; highest in sets 7 and 8 (post-digestion, summer 2018).
  • Cu: range approximately 0.45–0.95 mg·kg⁻¹ d.s.
  • Cr: range approximately 0.45–1.05 mg·kg⁻¹ d.s.
• Qualitative EDX spectrum (Figure 1, p. 5) additionally identified Fe, Mg, Na, K, Ca, S, P, Ti, Mn, Co, Zn, Sn, and Pb peaks; no quantitative values for these elements are reported.
• The Pearson correlation matrix for the sludge variables (Table 5, p. 10) shows weak inter-metal correlations: Cr³⁺–Ni²⁺ r = −0.31, Cr³⁺–Cu r = +0.37, Ni²⁺–Cu r = +0.34; the strongest correlations in the dataset are pH–N-total (r = +0.52) and N-total–K (r = +0.49).

Agricultural soil characterisation (Galati County)

Two soil types received the sludge; the cited values are averages across the 5-hectare collection units.

Soil-side heavy metal mapping (Figure 5, p. 8) is presented only as colour-graded county maps; the published legends bin the dispersion values into narrow ranges that the authors state fall within the regulatory ceilings cited below. Per-parcel numerical values are not provided.

Sludge application protocol

• Approximately 1.5 t sludge per hectare per application; 1.55–1.85 t calcareous amendment (calcite + dolomite mixture) per hectare per application; two applications per year on the same parcels (pp. 6, 11).
• Calcareous co-amendment is used as a CaCO₃–Ca(HCO₃)₂ buffer system (pKa ≈ 7.48) to keep amended-soil pH above 6.5 and so suppress heavy-metal mobility into crops (p. 11).
• Initial study area: 40 ha (p. 6).

Regulatory ceilings cited

For sewage sludge applied to agricultural land, Romanian Order 344/2004 (implementing Council Directive 86/278/EEC) sets the following maximum permitted heavy-metal concentrations in the sludge itself (p. 8):

• Cr³⁺: 500 mg·kg⁻¹ dry sludge.
• Ni²⁺: 100 mg·kg⁻¹ dry sludge.
• Cu²⁺: 500 mg·kg⁻¹ dry sludge.

These are sludge-side ceilings, not soil-side ceilings; the corresponding Romanian soil ceilings under Order 344/2004 are tighter (Cr 100, Ni 50, Cu 100 mg·kg⁻¹ DS) but are not cited in this paper. The authors state all measured sludge values fall well below the 500/100/500 sludge ceilings, and that the sludge-amended soils are within “EU and national legislation” without specifying which soil ceiling is being compared against (pp. 8, 11).

Methods (brief)

Sludge and soil sampling was performed in conformity with national reference methods listed by code only (Table 1, p. 3, and Table 2, p. 4). Heavy metal levels in the sludge were determined using atomic absorption spectroscopy (AAS), X-ray fluorescence (XRF), and spectrophotometric methods (p. 5); energy-dispersive X-ray spectroscopy (EDX) was used for qualitative elemental identification of the sludge solids (Figure 1, p. 5). Electrometric methods were used for pH and for additional physico-chemical parameters (p. 3). Specific standards invoked include SR EN 16192:2012 (Cr-total, Ni²⁺), SR 13179/93 (Cu²⁺), SR EN 12176 (pH), and SR ISO 11261:2000 (N-total).

Reported speciation: chromium is reported as Cr-total (the regulatory ceiling itself is written as Cr³⁺ but the analytical method given, SR EN 16192:2012, returns total Cr); Cu and Ni are reported as Cu²⁺ and Ni²⁺ in the regulatory language but the analytical methods listed (AAS, ICP-style standards) measure total metal. No mercury speciation was performed; mercury is mentioned only as one of the seven heavy metals required to be monitored under the implementing legislation, not as a measured value.

Limits of detection, limits of quantification, recovery for certified reference materials, replicate counts within each sample set, and analytical uncertainty are not reported. Statistical analysis used Principal Component Analysis (PCA) on the normalised dataset (Shapiro–Wilk for normality, log transformation otherwise) and Pearson correlation (Section 2.3, p. 4; Figures 6–7 and Table 5, pp. 9–10).

Implications

Certification: Provides a worked example, in a post-industrial Eastern European catchment, of municipal sludge entering the agricultural supply chain at heavy-metal concentrations well below the EU Sewage Sludge Directive ceilings. Useful background for HMT&C supplier-questionnaire design on soil-amendment history, but the per-element values reported here are too coarse (bar-chart reads, no LOD reporting, no replicate uncertainty) to anchor any quantitative supply-chain risk threshold.

Courses: Supports the “Why do agricultural soils contain heavy metals?” module as an illustrative case for the role of municipal wastewater de-industrialisation in lowering sludge-borne metal loadings. The CaCO₃–Ca(HCO₃)₂ buffer-system framing on pp. 11 is a useful classroom anchor for pH-driven metal mobility.

App: No direct ingredient-level data — the study measures sludge and soil, not finished foods. No ingredient contamination_profile contribution.

Verification notes

• 2026-06-03 merge-enhance pass on the June-2 initial ingest (iticescu2021-sewage-sludge-agricultural-land, committed in 4f31cc6). Preserved the original cite_key, raw_handle, raw_path, and doi. Replaced bespoke matrix slugs (municipal-sewage-sludge, sludge-amended-soil, calcareous-amendment, wastewater-treatment-plant-sludge) with controlled-vocabulary [sewage-sludge, agricultural-soil] per the system-prompt vocabulary; precedent set by [[sources/de-silva2023-industrial-waste-land-application-soil]] and [[sources/mozdzer2023-sludge-ash-granulates-crop-metals]]. Reformatted author list to Lastname I convention (was full first names). Downgraded evidence_tier from A to B given the absence of numerical heavy-metal tables, LOD/LOQ, and replicate statistics (Figure 3 reports metals only as an unlabelled bar chart). Added the post-amendment soil table, Pearson-correlation read-outs from Table 5, and the explicit regulatory citation (Directive 86/278/EEC + Romanian Order 344/2004).
• Frontmatter metals: [Cr, Cu, Ni] reflects what was quantitatively measured; the regulatory text on pp. 2–3 lists seven monitored elements (Cr, Cu, Ni, Pb, Zn, Cd, Hg) but only Cr, Cu, and Ni have reported values. Pb and other elements appear only as unlabelled peaks in the EDX spectrum (Figure 1).
• Frontmatter ingredients: [] and products: []: this is a sludge/soil characterisation paper, not a foodstuff measurement, and so does not contribute direct evidence to any ingredient or product page.
• Matrices sewage-sludge and agricultural-soil follow the existing controlled vocabulary used by sources such as [[sources/de-silva2023-industrial-waste-land-application-soil]] and [[sources/mozdzer2023-sludge-ash-granulates-crop-metals]].
• Evidence tier B: peer-reviewed open-access journal article, but the analytical reporting is thin (no LOD/LOQ, no replicate statistics, heavy-metal values published only in bar-chart and county-map form rather than tables), which keeps it below A-tier.
• Heavy-metal values in this page are read from Figure 3 of the article; the article does not publish a numerical table for those values. Spot-check by a second reader is welcome; flag any disagreement against the printed bars.
• 2026-06-03 audit (fresh-context subagent) flagged two items, both verified and applied: (a) the cited 500/100/500 mg·kg⁻¹ DS ceilings were originally framed as receiving-soil limits; the paper text on p. 8 actually frames them as sludge-side limits applied “to the sewage sludge used on agricultural land”, and the 500/100/500 values themselves match Romanian Order 344/2004 SLUDGE limits (not soil limits), so the section was rewritten. (b) XRF was omitted from the Methods list; the paper p. 5 explicitly names AAS + XRF + spectrophotometric as the heavy-metal methods; XRF added. One audit finding (Cu not in metals vocabulary list) was a false positive — Cu is the standard chemical symbol and matches usage on sources such as [[sources/de-silva2023-industrial-waste-land-application-soil]]; no change applied.

Wiki pages updated on ingest

• Chromium
• Copper
• Nickel
• soil-contamination-sources

Page history

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