The researchers collected eighteen sediment samples between February and July 2025 from El Harrach, Mohammadia, Bordj El Kiffan, and Oued Smar, four locations that have long absorbed the runoff of Algeria’s capital region. From that set, four representative samples — labeled S1 through S4 — were selected for detailed multi-analytical screening. The goal was not to solve a single pollution case but to build a baseline dataset that could support future source-discrimination studies, ecological risk assessment, and sediment quality monitoring.

The analytical strategy was deliberately broad. Thin-layer chromatography and gas chromatography–mass spectrometry were used to screen for organochlorine and organophosphorus pesticides. Fourier-transform infrared spectroscopy probed for phenolic signatures. Atomic absorption spectroscopy quantified heavy metals, and automatic thermal desorption gas chromatography–mass spectrometry hunted for hydrocarbons. Each technique was chosen for its ability to detect a specific class of contaminants at trace levels.

The pesticide results came back clean — at least under the applied screening conditions. No targeted organochlorine or organophosphorus pesticides were detected, and no FTIR-identifiable phenolic signatures were observed. The GC–MS method achieved compound-specific limits of detection ranging from 0.012 to 0.029 mg kg⁻¹ and limits of quantification from 0.036 to 0.088 mg kg⁻¹, meaning the instruments could reliably detect pesticides at extremely low concentrations. The researchers caution, however, that trace-level phenolic occurrence cannot be entirely excluded by the FTIR screening approach.

The heavy metal picture was dramatically different. Every sample contained measurable concentrations of cadmium, chromium, copper, iron, lead, nickel, and zinc, with notable spatial variability between sites. The geoaccumulation index, a measure that compares observed metal concentrations against natural background levels, indicated moderate to heavy contamination for selected metals. When compared against sediment quality guidelines, concentrations of lead, nickel, and zinc exceeded the probable effect level — a threshold above which adverse biological effects are likely to occur.

Perhaps most tellingly, the pollution load index exceeded unity at all four sites, a signal that the sediments are degraded across the board rather than at isolated hotspots. This is not a story of one rogue discharge but of chronic, widespread industrial pressure on an urban watershed. The combined metal–hydrocarbon profiles provide site-specific contamination fingerprints that clearly differentiate between sampling locations.

The hydrocarbon analysis added another layer to the forensic picture. Recurrent aliphatic compounds were detected in all samples, consistent with petroleum-derived or urban-industrial inputs. These findings align with the region’s long history of industrial activity, including petroleum refining, manufacturing, and dense urban runoff. The aliphatic profile — the specific pattern of hydrocarbon chain lengths — can serve as a diagnostic tool in future source apportionment studies, helping investigators distinguish between petrogenic sources, combustion-derived inputs, and other urban contributions.

What makes this study scientifically significant is its forensic framing. Rather than simply reporting contamination levels, the researchers treated the sediments as evidence in an ongoing environmental investigation. The combined metal–hydrocarbon profiles function as fingerprints — unique chemical signatures that can be matched against potential pollution sources in future targeted studies. This approach transforms routine monitoring data into actionable forensic intelligence.

The implications for the Algiers area are considerable. The Oued El Harrach watershed has been the subject of environmental concern for decades, with earlier studies documenting mercury and heavy metal contamination as far back as 2005. The new baseline dataset establishes a reference point against which future remediation efforts can be measured. As industrial activity continues and urbanization intensifies, the ability to track contamination fingerprints over time will be essential for protecting public health and ecosystem integrity in one of North Africa’s most densely populated regions.

For now, the sediments of Algiers continue to accumulate their chemical history, layer by layer. This study demonstrates that with the right analytical tools — and a forensic mindset — that history can be read, interpreted, and ultimately used to hold pollution sources accountable. The four sediment samples may represent just a preliminary screening, but they open a window onto the hidden chemistry of an industrialized urban landscape, one that will inform environmental forensics in the region for years to come.

The analytical choices made in the study reflect a tiered screening philosophy common in environmental forensics, where rapid, low-cost techniques are deployed first to narrow the field before more expensive confirmatory methods are applied. Thin-layer chromatography, for instance, has long been validated by the International Atomic Energy Agency as a practical screening tool for pesticide residue analysis in laboratories with limited instrumentation, and its use here alongside gas chromatography–mass spectrometry illustrates how complementary methods can cross-check one another. The absence of detectable organochlorine and organophosphorus pesticides is itself informative: organochlorine compounds such as DDT and lindane are notoriously persistent in sediments and are frequently reported in urban waterways of the Mediterranean basin, so their non-detection above the stated limits of detection suggests either genuine absence, degradation over time, or inputs below the quantifiable threshold.

The interpretation of the metal data rests on well-established geochemical indices, each with its own logic. The geoaccumulation index, introduced in the late 1960s, compares measured concentrations against a geochemical background value, typically using a factor of 1.5 to account for natural variation in background soils, and assigns contamination classes ranging from practically uncontaminated to extremely contaminated. The pollution load index takes a different approach, computing the geometric mean of contamination factors across all measured metals at a site, which makes it sensitive to the overall burden rather than any single element. A value above unity indicates progressive deterioration, and the fact that all four sites exceeded this threshold points to diffuse, catchment-wide metal loading rather than point-source hotspots.

Sediment quality guidelines add a biological dimension that pure geochemistry cannot provide. The probable effect level represents the concentration above which adverse effects on benthic organisms are frequently observed, while the threshold effect level marks concentrations below which effects are rarely expected. Exceedances of the probable effect level for lead, nickel, and zinc therefore carry direct ecological weight: these are concentrations at which toxicity to invertebrates living in or on the sediment becomes a realistic concern. Nickel and zinc exceedances are particularly common in industrialized estuaries, reflecting galvanized surfaces, alloys, fuels, and manufacturing waste, while lead in urban catchments often traces back to historical traffic emissions, paint, and industrial discharges that remain locked in fine-grained deposits.

The hydrocarbon findings connect the Algiers results to a broader body of Mediterranean sediment research. Aliphatic hydrocarbon distributions, particularly the relative abundances of n-alkanes of different chain lengths, have been used since the classic work of Bray and Evans in the early 1960s to distinguish petroleum-derived inputs from biogenic sources such as terrestrial plant waxes or algal production. A pattern dominated by unresolved complex mixtures and mid-chain alkanes typically signals weathered petroleum, whereas a strong odd-over-even predominance at longer chain lengths points to higher plant wax. The recurrent aliphatic compounds observed across all four samples, consistent with petroleum-derived or urban-industrial inputs, fit the expected signature for a catchment hosting refineries, transport infrastructure, and dense urban drainage.

The study also sits within a growing Algerian literature on coastal contamination. Previous work along the central Algerian coast has separated anthropogenic from geogenic trace element contributions in sediments, and sediment cores from Algiers Bay have documented the vertical history of trace metal deposition, showing how contamination intensified with industrialization. Studies around the rehabilitated Oued Smar dump have likewise reported elevated heavy metal degrees in surrounding soils, which makes the elevated metal burden at that site in the present screening consistent with prior findings rather than an anomaly. This convergence across independent studies strengthens confidence that the fingerprints identified here reflect real, persistent environmental conditions rather than sampling artifacts.

Methodologically, the combination of automatic thermal desorption with gas chromatography–mass spectrometry deserves note. Thermal desorption allows volatile and semi-volatile hydrocarbons to be transferred from the sample directly into the chromatographic system without extensive solvent extraction, reducing blank contamination and improving sensitivity for light hydrocarbon ranges that conventional solvent methods can miss. This makes the technique well suited to screening work where sample throughput and contaminant breadth matter more than exhaustive speciation of every compound class.

The forensic framing also anticipates the statistical tools that typically follow such screening exercises. Principal component analysis and related multivariate methods are standard next steps for apportioning metal sources, grouping elements that behave coherently and linking them to plausible emission categories such as industrial discharge, vehicular traffic, or natural weathering. The authors’ baseline dataset, with its site-specific metal and hydrocarbon profiles, provides exactly the kind of structured input such analyses require. As more sampling campaigns accumulate, temporal comparison against this baseline will reveal whether remediation measures, changes in industrial activity, or urban expansion are shifting the contamination signatures of the watershed.

For environmental managers, the practical takeaway is that sediment monitoring in the Algiers area should prioritize the metals flagged by guideline exceedances while maintaining surveillance for hydrocarbon inputs. Sediments act as both sinks and secondary sources: contaminants buried during decades of industrial activity can be remobilized by dredging, flooding, or changing water chemistry, meaning today’s baseline is not merely a historical record but a predictor of future exposure pathways for the aquatic food web and, indirectly, for the human communities along the Oued El Harrach and the bay.

Subject of Research: Multi-analytical screening of pesticides, phenols, heavy metals, and hydrocarbons in sediments from industrialized sites: a preliminary forensic interpretation

Article Title: Multi-analytical screening of pesticides, phenols, heavy metals, and hydrocarbons in sediments from industrialized sites: a preliminary forensic interpretation

Article References: Loutis, M., Meftali, D., Benayad, T., Djellouli, F., & Dahmani, A. (2026). Multi-analytical screening of pesticides, phenols, heavy metals, and hydrocarbons in sediments from industrialized sites: a preliminary forensic interpretation. Environmental Monitoring and Assessment, 198(11), Article 1213. https://doi.org/10.1007/s10661-026-16055-w

Image Credits: AI Generated

DOI: 10.1007/s10661-026-16055-w

Keywords: Multi-analytical, screening, pesticides, phenols, heavy, metals, hydrocarbons, sediments, industrialized, sites, preliminary, forensic