Trends in Polychlorinated Biphenyl Contamination in Bucharest’s Urban Soils: A Two-Decade Perspective (2002–2022)

Abstract

Polychlorinated biphenyls (PCBs) are synthetic organic compounds that were widely used in industrial applications throughout the 20th century. Due to their chemical stability, resistance to degradation and ability to bioaccumulate and biomagnify through food chains, PCBs pose long-term environmental and health risks. Due to these characteristics, PCBs have been globally regulated as persistent organic pollutants (POPs), despite being banned from production in most countries decades ago. This study investigates temporal trends in PCB contamination in urban soils of Bucharest over a 20-year period (2002–2022), focusing on six principal congeners (PCB 28, 52, 101, 138, 153, and 180) sampled from 13 locations, including roadsides and urban parks. Gas chromatography and spatial analysis using inverse distance weighting (IDW) revealed a marked reduction in Σ6PCB concentrations, declining from 0.0159 mg/kg in 2002 to 0.0065 mg/kg in 2022, with statistically significant differences confirmed by Kruskal–Wallis analysis (p < 0.05). This decline is primarily attributed to reduced emissions, source control measures, and natural attenuation. However, the persistence of PCBs in localized hotspots is influenced by secondary dispersion mechanisms, such as atmospheric deposition and surface runoff, which redistribute contaminants rather than eliminate them. Health risk assessments via ingestion, dermal absorption, and inhalation routes confirmed negligible carcinogenic risk for both adults and children. Although measurable progress has been achieved, the persistence of localized contamination underscores the need for targeted remediation strategies and sustained environmental monitoring to protect vulnerable urban areas from recontamination.

1. Introduction

Persistent organic pollutants (POPs) are hazardous chemicals that are characterized by their remarkable resistance to environmental degradation, their ability to be transported over long distances in the atmosphere and their strong tendency to bioaccumulate in living organisms. These properties have facilitated their global dispersion and prolonged persistence in ecosystems, where they pose serious risks to both human health and ecological integrity [1,2,3]. Despite international regulatory efforts (Figure 1), POPs continue to be widely distributed in the environment due to legacy emissions, inappropriate disposal practices and continued releases from secondary sources [4,5,6,7]. Over the years, a series of international policy milestones has gradually shaped the legal framework aimed at controlling, reducing, and ultimately eliminating emissions of persistent organic pollutants, including polychlorinated biphenyls (PCBs). A key element of this global effort is the Stockholm Convention on Persistent Organic Pollutants, which entered into force in May 2004. The Convention’s primary objective is to protect human health and the environment by eliminating the production, use, and trade of POPs. As of today, it has been ratified by 185 parties [8], reflecting a broad and sustained international commitment.

PCBs are specifically listed under Annexes A and C of the Convention, which imposes binding obligations on parties to take comprehensive action against their production and use. Under these provisions, parties are required to ban the production and prohibit the introduction of new uses of PCBs, thereby supporting global elimination objectives. Additionally, all parties must undertake determined efforts to identify, label, and phase out equipment containing PCBs, such as transformers, capacitors, and other devices with liquid PCB stocks, by the year 2025. Beyond this deadline, the Convention mandates that all materials contaminated with PCBs, particularly those with concentrations exceeding 0.005% (50 mg/kg), must be managed in an environmentally sound manner (ESM), with complete elimination required no later than 2028. The parties are also encouraged to identify and properly manage open applications that may contain PCBs (e.g., in sealants, paints, or electrical cables). Moreover, the export and import of PCBs is only permitted for the purposes of environmentally sound waste management.

Despite these well-defined goals, implementation has faced significant challenges. According to the most recent global assessment, only 17% of the estimated global PCB stockpile has been safely eliminated, leaving approximately 14 million tonnes—equivalent to 83%—still awaiting proper treatment and disposal [9].

Polychlorinated biphenyls (PCBs) have received particular attention because of their widespread historical usage and toxicological significance. Used extensively from the 1930s to the 1980s in electrical equipment, hydraulic systems, paints, and building materials [10], PCBs were prized for their thermal stability, fire resistance, and dielectric properties [11,12]. However, these same characteristics contribute to their environmental longevity and difficulty of remediation. Although significant regulatory progress has been made, PCBs continue to contaminate various environmental matrices, including soils, sediments, water bodies [6,13,14,15,16], agricultural zones [17,18,19], and urban areas worldwide [20,21]. In addition to historical usage, PCBs are still unintentionally generated through current industrial activities. Processes such as waste incineration, metallurgical refining, and cement production contribute to PCB formation via de novo synthesis mechanisms [22,23,24]. These secondary sources exacerbate global contamination levels, complicating management strategies. Their persistence in the environment, coupled with their endocrine disruption, metabolic disorders, liver damage, and carcinogenic potential [7,25,26,27], has intensified scientific focus on their occurrence, distribution, and long-term impacts [28,29,30,31].

Polychlorinated biphenyls comprise a group of 209 individual congeners, each differing in the number and position of chlorine atoms on the biphenyl molecule. These structural variations influence their physical, chemical, and toxicological properties [27,32]. PCB mixtures can vary in appearance, from light-colored mobile liquids to yellow or black waxy solids, depending on their degree of chlorination. Congeners with a higher chlorine content tend to be more persistent, strongly lipophilic, and are more commonly detected in biota and food chains. In contrast, lower-chlorinated PCBs are semi-volatile, more mobile, and tend to degrade more rapidly under environmental conditions. These characteristics significantly influence their environmental distribution and human exposure profiles.

To contextualize the present study, it is essential to consider global contamination patterns and the evolving strategies for PCB remediation, which are shaped by the varying behaviors and risks associated with different PCB congeners. Polychlorinated biphenyls, particularly low-chlorinated biphenyls (LCBs), have been widely detected in urban and industrial soils around the world due to their persistence, mobility, and historical usage. Numerous studies have shown that despite global bans and declining emission trends, soil contamination remains a serious concern. In developed countries, such as the United Kingdom and the United States, concentrations in soil have reached up to 50 mg/kg [33,34,35]. In Central London, the normalized baseline concentration (NBC) for Σ7PCBs (110 µg/kg) and PCB 118 (59 µg/kg) exceeded residential and allotment guideline values [36]. In Nigeria, improper disposal of PCB-containing transformers has led to serious pollution in soil and water [37]. In China, elevated PCB levels have been found in coastal and agricultural zones, with concentrations in farmland soils ranging from 0.00005 to 0.4845 mg/kg [35,38,39]. Industrial areas tend to show significantly higher contamination than agricultural land [23,40,41].

To manage PCB-contaminated soil, various remediation technologies have been explored, including physical (e.g., soil washing, incineration), chemical (e.g., oxidation, dechlorination), and biological methods (e.g., microbial degradation, phytoremediation) [42,43,44,45,46,47,48]. Each method has strengths and limitations related to cost, site conditions, and environmental impact. Recently, integrated approaches combining chemical pretreatment with biological remediation have shown promising results in laboratory and pilot-scale trials [49], though field-scale implementation remains limited.

Long-term studies have shown that even non-industrial sources, such as PCB-containing building materials, can contribute significantly to soil contamination. Herrick et al. (2007) [50] demonstrated that caulking used in older buildings can leach PCBs into adjacent soils, leading to exposure risks in schools and residential settings.

In Bucharest, Romania’s largest urban and industrial center, multiple legacy sources, including outdated electrical infrastructure, improper waste disposal, and atmospheric deposition, continue to contribute to PCB soil contamination [51,52,53]. While earlier investigations have confirmed the presence of PCBs in Bucharest’s urban soils and associated human health risks [54,55], these studies have typically focused on isolated time points or industrial hotspots. As such, there is a lack of comprehensive, long-term datasets capturing the temporal evolution of contamination across diverse land-use categories. This gap is particularly relevant given the persistence of PCBs and the absence of routine soil monitoring in the region. Additionally, most existing studies have focused on industrial hotspots, while urban environments with diffuse sources remain underexplored. There is a pressing need to establish long-term datasets for urban areas in Central and Eastern Europe to assess contamination trends, inform policy, and guide effective remediation and land-use planning.

Addressing this gap, the present study builds on a longitudinal monitoring initiative spanning two decades (2002–2022) and analyzes six major PCB congeners (28, 52, 101, 138, 153, 180) in urban soil samples. The main objectives are to (1) assess long-term contamination trends, (2) identify persistent hotspots, (3) assess health risks for children and adults, and (4) compare results with national and global benchmarks. By combining spatial interpolation techniques and USEPA standard health risk assessments, this study provides a comprehensive insight into PCB dynamics in the urban environment of Bucharest.

2. Materials and Methods

2.1. Study Area

Bucharest, the capital of Romania, is the country’s largest urban and industrial center, with a population of approximately 1.71 million inhabitants according to the 2021 census [56]. Spanning over 240 km², the city has undergone intense industrialization, rapid urban expansion, and sustained traffic congestion since the mid-20th century. Its humid continental climate—characterized by pronounced seasonal variations and temperature extremes—further influences the mobility, transformation, and long-term persistence of semi-volatile pollutants, such as polychlorinated biphenyls. Historically, PCBs were extensively used in Bucharest across a wide range of applications, including electrical equipment, construction materials, and energy systems. Due to inadequate waste management practices, outdated electrical infrastructure, and unintentional emissions from industrial processes, PCBs have accumulated in urban soil and remain persistent despite regulatory restrictions. As such, Bucharest exemplifies the environmental legacy of post-industrial Eastern European cities, where diffuse and localized sources of pollution continue to pose significant ecological and public health risks.

Previous research has confirmed the presence of PCBs in various urban zones of Bucharest, including both residential and recreational areas. Notably, studies conducted in 2002 and 2012 identified widespread soil contamination, with PCB concentrations in several locations exceeding the intervention thresholds set by Romanian Ministry Order No. 756/1997 [51,52,53]. These findings have been supported by subsequent risk assessment studies, which identified ingestion and dermal contact as the primary exposure pathways, and in certain areas, documented carcinogenic risks above acceptable levels [54,55].

Despite these prior investigations, there is a lack of long-term, systematic, city-wide assessments that explore both spatial and temporal trends of PCB contamination in urban soils. Given the known persistence and health impacts of these compounds, continuous monitoring is essential to evaluate their behavior and inform appropriate land-use policies and risk mitigation strategies. The present study aims to address this gap by building upon previous efforts and extending the scope to cover a 20-year timeframe (2002–2022), using congener-specific chemical analysis, spatial interpolation, and human health risk assessments.

2.2. Sources of PCBs in Bucharest

Although PCBs were banned under the 2004 Stockholm Convention, they continue to be present in Bucharest due to a combination of legacy contamination, aging infrastructure, and ineffective waste management practices. Estimating source contributions remains challenging due to data gaps.

2.2.1. Industrial Legacy and Former Manufacturing Facilities

Numerous industrial platforms formerly operated in Bucharest, Romania, used PCBs in electrical equipment, hydraulic fluids, adhesives, and coatings. The major contributors included heavy industry (Electroaparataj, IMGB), chemical plants (Policolor), and aviation and automotive facilities (Turbomecanica). Many of these sites were abandoned after 1989 without decontamination, resulting in long-term soil contamination.

2.2.2. Waste Disposal and Landfills

Improper disposal of PCB-laden construction and industrial waste at unregulated landfills has been a major source of contamination. Open burning has further dispersed PCBs into the atmosphere.

2.2.3. Soil and Atmospheric Deposition

PCB accumulation is significant in industrial areas, such as Militari, Pipera, and Băneasa, with redistribution through atmospheric deposition and roadside dust. Residential developments near legacy sites remain at risk due to remobilization of semi-volatile PCBs across air, water, and soil.

2.3. Soil Sampling and Preparation (Data Collection Methodology)

This study is part of a long-term monitoring program designed to assess the presence and temporal evolution of polychlorinated biphenyls (PCBs) in urban soils of Bucharest. Soil sampling was carried out across three key years—2002, 2012, and 2022—allowing for comparative analysis of contamination trends over a 20-year period.

The most recent sampling campaign, conducted in the summer of 2022, adhered strictly to the methodological protocols established in the earlier studies, including consistent sampling depth, sample preparation, and analytical procedures. This ensured full data comparability across all three times.

Sampling in 2022 was performed at 13 sites that had previously recorded PCB concentrations above regulatory thresholds in both 2002 and 2012. These locations represent a range of urban land uses, including roadside areas and public parks (

Table 1. Localization and general information on investigated soils.

Sample Code	Sampling Location	Latitude (N)	Longitude (E)
P13 1	Piaţa C.A. Rosetti	44°26′10.83372″ N	26°6′23.6052″ E
P29 1	Kiseleff (0.5 m)	44°28′10.0862″ N	26°4′38.31924″ E
P30 1	Kiseleff (7 m)	44°28′10.9142″ N	26°4′38.432″ E
P31 1	Băneasa Neagoe Vodă street	44°29′34.20852″ N	26°4′53.93244″ E
P37 1	Dudu	44°27′40.27464″ N	25°59′9.6036″ E
P38 1	Roşu	44°27′12.26196″ N	25°59′35.01924″ E
P40 1	Tricodava	44°25′10.12584″ N	26°2′5.8272″ E
P41 1	Lujerului	44°26′3.60564″ N	26°2′2.3244″ E
P42 1	Giuleşti Sârbi 540–542	44°28′29.97372″ N	26°0′0.27756″ E
P44 1	Giuleşti Sârbi 538	44°28′26.62212″ N	25°59′59.86725″ E
P32 2	Băneasa Zoo	44°31′4.71288″ N	26°6′8.77212″ E
P35 2	Străuleşti	44°30′11.1438″ N	26°1′28.90848″ E
P36 2	Bazilescu	44°29′18.22308″ N	26°2′10.45104″ E
P39 2	Drumul Taberei	44°25′20.52456″ N	26°2′17.3212″ E

Note: Sampling point codes reflect the original identifiers used in the 2002 and 2012 monitoring campaigns, retained here to ensure consistency in long-term trend analysis. These locations were selected based on previously recorded exceedances of Romanian regulatory thresholds for PCBs. ¹ Roadside soil, ² Park soils.

; Figure 2). The datasets from 2002 and 2012 were obtained from earlier field studies conducted and published by our research team (Preda et al., 2010; Sandu et al., 2013) [51,53]. The sampling point codes (e.g., P13, P29, etc.) were maintained from the previous monitoring campaigns conducted in 2002 and 2012. These specific sites were selected based on historically elevated PCB concentrations exceeding Romanian regulatory thresholds. To ensure consistency and allow for accurate temporal comparisons, the original numbering was preserved.

At each site, five subsamples were collected from the topsoil (0–10 cm depth) within a 10 m² plot using a stainless-steel Dutch auger. Prior to compositing, visible surface debris, including plant material, gravel, and wood fragments, was carefully removed. At each site, approximately 1 kg of homogenized composite soil was collected, sealed in airtight polyethylene bags, and transported under cooled and stable conditions to the laboratory to ensure sample integrity, in accordance with ISO 10381-1:2002 [57].

In the laboratory of the National Institute of Research-Development for Pedology, Agrochemistry and Environmental Protection (ICPA) in Bucharest, soil samples were air dried at room temperature until a constant weight was achieved. The dried soils were then sieved to <2 mm to eliminate coarse particles and thoroughly homogenized in preparation for subsequent analytical procedures.

2.4. PCBs Extraction and Analysis

Polychlorinated biphenyls were extracted and analyzed at the ICPA Bucharest laboratory, following established protocols [58] and U.S. EPA Method 8082A [59]. Approximately 20 g of air-dried soil was subjected to solvent extraction using a 2:1 (v/v) petroleum ether/acetone mixture at 60 °C for 30 min. The extracts were subsequently washed with sodium sulfate solution to remove acetone residues, dried over anhydrous sodium sulfate, and concentrated. For cleanup, the concentrated extracts were purified using a Florisil (Supelco, Bellefonte, PA, USA) column, with hexane as the elution solvent to isolate PCBs from co-extracted organic matter, in accordance with EPA SW-846 guidelines. Quantitative determination was performed using a Carlo Erba Mega 5380 (Carlo Erba, Milan, Italy) gas chromatograph equipped with an electron capture detector (GC-ECD) and an OV-1 fused silica capillary column (50 m × 0.32 mm), following the specifications outlined in EPA Method 8082A for PCB detection. The chromatograph operated under the following temperature program: initial hold at 100 °C for 1 min, ramped at 10 °C/min to 180 °C (held for 2 min), then increased at 3 °C/min to 280 °C, with a final hold of 10 min. The injector temperature was set at 250 °C, and the detector temperature at 300 °C. Helium was used as carrier gas, and nitrogen served as the makeup gas. The quantification of specific PCBs was performed by comparing the peak areas of the samples to those of known standards. Calibration was performed using certified PCB congener standards, and quality control included blanks and spike recoveries to ensure analytical reliability.

To ensure analytical reliability, a comprehensive quality control (QC) protocol was applied throughout the study. Certified reference materials (CRMs) were employed to validate instrument calibration and performance. Recovery rates for CRMs ranged from 87% to 108%, in accordance with the EPA Method 8082A acceptance criteria. Procedural blanks were included in every analytical batch to detect potential contamination introduced during sample processing. Acceptable blank levels were defined as less than 50% of the lowest method reporting limit. Each soil sample was analyzed in triplicate to ensure reproducibility and minimize analytical variability.

The analytical focus was on six indicator PCB congeners, selected based on their chlorination degree and IUPAC designation: PCB 28 (tri-CB), PCB 52 (tetra-CB), PCB 101 (penta-CB), PCB 138 and PCB 153 (hexa-CBs), and PCB 180 (hepta-CB). Total PCB concentrations (Σ6PCB) were derived from the cumulative sum of these congeners.

2.5. Statistical Methods

To evaluate temporal trends and differences in PCB concentrations across the three sampling years (2002, 2012, and 2022), two statistical approaches were applied. Linear regression analysis was used to assess trends for each PCB congener, determining the direction and significance of concentration changes over time. The strength of these relationships was evaluated using the coefficient of determination (R²) and p-values, helping to identify which congeners showed statistically significant reductions.

In addition, a Kruskal–Wallis statistical analysis, a nonparametric alternative to one-way ANOVA, was performed to compare the median PCB concentrations across the three years. This statistical analysis was chosen due to the limited sample size and the potential for non-normal distribution of environmental data [60]. It allowed an assessment of whether observed differences in PCB concentrations over time were statistically significant without assuming normality.

2.6. Spatial Modelling Interpolation

Datasets obtained from field sampling were spatially interpolated using the Inverse Distance Weighting (IDW) method, implemented via the ArcMap 10.3 (Esri, Redlands, CA, USA) Geostatistical Analyst extension. IDW is a widely adopted deterministic interpolation technique in environmental science, geology, and meteorology for constructing continuous spatial surfaces from discrete point data [61]. It has proven effective in applications such as mapping air pollution, predicting rainfall, and estimating soil contamination levels [62,63].

The IDW method estimates values at unsampled locations by applying weights to known data points based on inverse proportionality to their distance from the target location—thus, closer points exert greater influence [64]. A key parameter in this method is the power factor, which determines how sharp distance influences weighting. Higher power values generate surfaces that closely follow localized variations but may introduce spatial noise, whereas lower values produce smoother, more generalized surfaces. IDW was chosen for this study due to its computational simplicity, reproducibility, and suitability for visualizing spatial patterns of environmental contamination. Unlike more complex geostatistical methods, such as Kriging, IDW does not require assumptions regarding data normality or spatial autocorrelation. This makes it particularly appropriate for uneven sampling networks, which are typical in urban soil pollution assessments. The method’s transparent and intuitive logic also facilitates the identification of PCB concentration hotspots across Bucharest.

It should be noted that the spatial distribution of the sampling points is uneven, with limited representation in the eastern and southern areas of Bucharest. As a result, the IDW interpolation maps should be interpreted as general visualizations of spatial trends rather than precise estimations of PCB concentrations at unsampled locations. This approach was chosen to maintain consistency with previous monitoring campaigns, although future studies would benefit from expanded and more evenly distributed sampling to enhance interpolation accuracy.

2.7. Health Risk Assessment Methodology

2.7.1. Exposure Assessment

The U.S. Environmental Protection Agency (USEPA) health risk assessment framework was applied to evaluate human exposure to polychlorinated biphenyls (PCBs) in Bucharest’s urban soils via three principal exposure pathways: (i) ingestion of contaminated soil particles; (ii) dermal absorption through direct skin contact; and (iii) inhalation of resuspended soil-derived particulates. This methodology adheres to the guidelines outlined in the USEPA’s Risk Assessment Guidance for Superfund and is consistent with protocols employed in recent environmental risk assessments [65,66,67].

The average daily dose (ADD; mg·kg⁻¹·day⁻¹) for each exposure pathway was estimated using standard Equations (1)–(3), as recommended by the USEPA for human health risk assessments [37].

$${ADD}_{ingestion}={\displaystyle \frac{C_{soil}\times IngR\times EF\times ED\times CF}{BW\times AT}}$$

(1)

$${ADD}_{inhalation}={\displaystyle \frac{C_{soil}\times InhR\times EF\times ED\times CF}{PEF\times BW\times AT}}$$

(2)

$${ADD}_{dermal}={\displaystyle \frac{C_{soil}\times SA\times AF\times ABS\times EF\times ED\times CF}{BW\times AT}}$$

(3)

where ADDI_ingestion, ADD_inhalation, and ADD_dermal represent the estimated exposure doses (mg·kg⁻¹·day⁻¹) via ingestion, inhalation, and dermal contact, respectively. C_soil denotes the concentration of PCBs in soil (mg·kg⁻¹). A complete description of all parameters, along with their values and references, is provided in

Table 2. Exposure parameters and values used in health risk assessment.

Symbol	Parameters	Selected Values
		Adults	Children
CF	Conversion factor (kg·mg−1)	10−6	10−6
EF	Exposure frequency (days years −1)	40	40
ED	Exposure duration (years)	24	6
BW	Body weight (kg)	70	15
AT	Averaging time, non-carcinogenic/carcinogenic (days)	8760/25,550	2190/25,550
IngR	Ingestion rate of soil particle (mg·day−1)	100	200
SA	Contact surface area of skin with soil (cm2)	5700	2800
AF	Soil-to-skin adherence factor (mg·cm−2)	0.07	0.2
ABS	Dermal absorption factor (%)	0.13	0.13
InhR	Inhalation rate (m3·day−1)	16	8
PEF	Particle emission factor (m3·kg−1)	1.36 × 109	1.36 × 109

[68,69,70,71,72,73,74].

Although the structure of Equations (1)–(3) remains standardized across exposure pathways, each equation incorporates pathway-specific parameters (e.g., InhR for inhalation; SA, AF, and ABS for dermal contact) and population-specific values (adults vs. children) as listed in Table 2. This approach ensures that the ADD is calculated using the most relevant biological and behavioral assumptions for each exposure route in accordance with USEPA guidance.

2.7.2. The Carcinogenic Risk

To estimate carcinogenic risk, the average daily dose (ADD) for each exposure pathway was multiplied by the corresponding carcinogenic slope factor (SF), as follows:

RISK_i = ADD_i × SF_i

(4)

RISK_T = ∑SF_i

(5)

where RISK_i represents the carcinogenic risk from each individual exposure pathway (dimensionless); RISK_T is the cumulative carcinogenic risk from all pathways; and SF_i is the slope factor for carcinogenesis via ingestion, dermal, or inhalation exposure (in kg·d·mg⁻¹). The SF value of PCBs is 2 kg·d·mg⁻¹ for ingestion and the dermal route, and 2.18 × 10⁻³ kg d·mg⁻¹ for inhalation. These values are derived from USEPA guidelines and represent upper-bound estimates of the probability of developing cancer over a lifetime of exposure. According to the U.S. Environmental Protection Agency [75], a cancer risk range between 1 × 10⁻⁶ and 1 × 10⁻⁴ is considered acceptable for regulatory purposes.

2.7.3. The Non-Carcinogenic Risk

To assess potential non-carcinogenic health risks, the hazard quotient (HQ) was calculated for each exposure route, and the cumulative risk was expressed as the hazard index (HI):

$${HQ}_i={\displaystyle \frac{{ADD}_i}{{RfD}_i}}$$

(6)

$$HI=\sum {HQ}_i$$

(7)

where HQ_i is the non-carcinogenic risk from a specific exposure pathway (dimensionless); HI is the total non-carcinogenic risk across all pathways, nondimensional; and RfD_i is the reference dose for each exposure route (mg·(kg·day)⁻¹), representing the daily exposure level unlikely to cause adverse health effects over a lifetime. For PCBs, the reference dose (RfD) is 2.3 × 10⁻⁵ mg·(kg·day)⁻¹, based on USEPA guidelines [75]. An HI value below 1 is considered within the acceptable range, while values exceeding 1 may indicate potential health concerns requiring further evaluation.

3. Results

This section presents a comprehensive evaluation of polychlorinated biphenyl concentrations in urban soils of Bucharest across three sampling periods: 2002, 2012, and 2022. It examines congener-specific behavior, statistical patterns, spatial distribution, and associated health risks—highlighting both the persistence and spatio–temporal variability of PCB contamination in the urban environment.

3.1. Congener-Specific Trends

Table 3. Descriptive statistics of PCB congener concentrations (mg·kg⁻¹) in Bucharest soils across three sampling years (2002, 2012, 2022).

PCB Congener	2002				2012				2022
	Minimum	Maximum	Mean	Std. Deviation	Minimum	Maximum	Mean	Std. Deviation	Minimum	Maximum	Mean	Std. Deviation
PCB 28	0.0000	0.0020	0.0018	0.0009	0.0000	0.0018	0.0010	0.0007	0.0000	0.0000	0.0000	0.0000
PCB 52	0.0012	0.0078	0.0029	0.0025	0.0000	0.0070	0.0029	0.0023	0.0010	0.0050	0.0020	0.0013
PCB 101	0.0007	0.0020	0.0012	0.0007	0.0017	0.0090	0.0034	0.0034	0.0010	0.0080	0.0010	0.0030
PCB 138	0.0002	0.0345	0.0038	0.0104	0.0006	0.0180	0.0046	0.0060	0.0010	0.0100	0.0015	0.0028
PCB 153	0.0005	0.0300	0.0060	0.0102	0.0004	0.0200	0.0043	0.0068	0.0010	0.0130	0.0010	0.0039
PCB 180	0.0004	0.0542	0.0075	0.0169	0.0008	0.0406	0.0072	0.0124	0.0010	0.0370	0.0020	0.0121
Ʃ6PCBs	0.0011	0.1180	0.0159	0.0393	0.0018	0.0774	0.0167	0.0268	0.0010	0.0590	0.0065	0.0181

presents the statistical distribution of individual PCB congeners across the three sampling years (2002, 2012, and 2022). A general decline in total PCB concentrations (Σ6PCBs) was observed, decreasing from 0.0159 mg/kg in 2002 to 0.0167 mg/kg in 2012, followed by a significant reduction to 0.0065 mg/kg in 2022. PCB 28 demonstrated a consistent decline, reaching non-detectable levels by 2022, which suggests effective degradation or source elimination. In contrast, PCB 52 remained relatively stable over time, indicating a persistent low-level presence. The higher-chlorinated congeners—PCB 101, 138, 153, and 180—exhibited fluctuating trends, likely due to differences in persistence, mobility, and potential ongoing sources. A reduction in standard deviation values in 2022 indicates a decrease in spatial variability, possibly reflecting improved environmental management. Among the congeners, PCB 180 consistently recorded the highest concentrations across all three years, underscoring its persistence and tendency for long-term accumulation.

Figure 3 illustrates the concentration gradients of individual PCB congeners and total Σ6PCB across the three sampling years. Detailed concentration values recorded at each time point are presented in Table S1.

In 2002 (Figure 3), low-chlorinated congeners, such as PCB 28, were generally detected at concentrations below the normal threshold established by MO 756/1997 [76] (0.0001 mg/kg). However, isolated exceedances were observed between the normal and warning thresholds. For instance, sample P1 recorded a concentration of 0.0081 mg/kg, surpassing the normal threshold yet remaining below the warning limit of 0.0020 mg/kg, warranting continued surveillance. In contrast, PCB 52 presented more notable concerns, with values at several sites (P13, P29, P40, and P41) falling within the warning threshold range. PCB 101 concentrations largely remained within acceptable levels, although a few instances approached the warning limit. Hexachlorobiphenyls, namely PCB 138 and PCB 153, exceeded the normal threshold across all sites and surpassed the warning threshold (0.01 mg/kg) at multiple locations, including P13, P29, P30, and P36. PCB 180, a high-chlorinated and persistent congener, frequently exceeded the normal threshold and, at some sites, also surpassed the intervention threshold of 0.04 mg/kg. This was particularly evident at site P29, where levels reached 0.0542 mg/kg, indicating a need for immediate remediation. Overall, total PCB concentrations (Σ6PCBs) exceeded the normal threshold in ten out of the thirteen locations sampled.

In 2012 (Figure 3), PCB 28 concentrations remained relatively stable, with the majority of sampling sites recording values below the normal threshold. A slight elevation was observed at site P30, where levels reached 0.0081 mg/kg. PCB 52 exhibited a modest increase in the number of locations falling within the warning threshold range, notably at P13, P29, P30, P38, P40, and P42. The concentration trends for PCB 101 varied, showing an increase at P30 while declining at sites P29, P31, and P36. Levels of hexachlorobiphenyls (PCB 138 and PCB 153) declined slightly relative to 2002 but remained above the warning threshold at P13, P29, P30, and P36. PCB 180 demonstrated a notable decrease at P30, declining from 0.0379 mg/kg in 2002 to 0.028 mg/kg in 2012; however, site P29 continued to exceed the intervention threshold. Overall, Σ6PCB concentrations showed a downward trend, with reduced levels observed at most sampling locations compared to 2002.

In 2022 (Figure 3), PCB 28 concentrations stayed below the normal threshold across all sites. PCB 52 continued to fall within the warning range at P13, P29, P30, P32, P35, P38, and P40, with minor fluctuations. Slight reductions in PCB 101 were noted, although levels at P30 remained in the warning range. PCB 138 and PCB 153 showed considerable improvement, with most concentrations falling below the warning threshold, though P29 remained elevated. PCB 180 levels declined across most locations but still hovered within the warning range in some areas. Total PCB concentrations dropped further, with most sites falling below warning thresholds, indicating an encouraging trend in contamination reduction.

Overall, these results demonstrate the complex behavior of PCB congeners in urban soils. While significant reductions have occurred, particularly for PCB 28, persistent hotspots at P29 and P30 underscore the need for continued monitoring and localized remediation. The observed congener-specific patterns may be influenced by several factors, including differences in degradation rates, with lower-chlorinated congeners (e.g., PCB 28) more prone to volatilization and microbial breakdown versus the stronger persistence and soil-binding affinity of higher-chlorinated congeners (e.g., PCB 180). Additionally, localized conditions, such as soil organic content, aeration, and ongoing emissions in traffic-dense zones (e.g., P29 and P30), likely contribute to the persistence of contamination at specific sites.

3.2. Overall Trends in PCB Contamination (2002–2022)

Longitudinal analysis of PCB concentrations from 2002 to 2022 reveals a consistent and encouraging decline across all monitored sites (Figure 4). Particularly significant reductions were observed at historically high-risk locations, such as P13, P29, and P30, where concentrations had previously exceeded critical thresholds. By 2022, PCB levels at the majority of sites had dropped well below regulatory warning limits, with P40, P41, and P42 demonstrating especially low concentrations. This downward trend reflects the cumulative impact of several distinct factors. First, regulatory enforcement, such as the national ban on PCB use and the implementation of environmental monitoring policies, has significantly reduced new inputs of PCBs into the environment. Second, infrastructure updates, including the replacement of outdated electrical equipment and improved waste management practices, have helped eliminate important legacy sources of PCB emissions. Third, natural attenuation processes, including photodegradation, microbial degradation, and volatilization (particularly of lower-chlorinated congeners), have contributed to the gradual reduction in PCB concentrations in surface soils over time. Together, these processes underscore the meaningful progress achieved in mitigating PCB contamination across Bucharest’s urban landscape.

To further elucidate the compositional dynamics of polychlorinated biphenyls (PCBs) in Bucharest’s urban soils, pie charts illustrating the relative contributions of individual congeners to total Σ6PCBs were constructed for the years 2002, 2012, and 2022 (Figure 5). These visualizations offer a concise snapshot of how the congener profile has shifted over the past two decades. The data indicate that PCB 180, a highly chlorinated and environmentally persistent congener, consistently dominated the congener composition in all three years. In 2012, its proportional share increased noticeably, likely due to the progressive degradation or volatilization of lower-chlorinated congeners, such as PCB 28 and PCB 52. Although total PCB concentrations declined by 2022, PCB 180 continued to represent the largest fraction of the Σ6PCBs, reinforcing its chemical stability, low volatility, and strong sorption affinity to soil particles. This trend underscores the importance of congener-specific analyses in environmental risk assessments. It also suggests that targeted remediation strategies should prioritize persistent, high-risk congeners like PCB 180 to effectively reduce long-term contamination and exposure risks.

3.3. Statistical Results

3.3.1. Regression Analysis

Regression analysis was applied to evaluate temporal trends in the concentrations of individual PCB congeners over the sampling years 2002, 2012, and 2022. This method enabled the identification of statistically significant declines and persistent patterns across the dataset (

Table 4. Regression analysis for PCB congener trends across 2002–2022.

PCB Congener	Coefficient	p-Value	R2	Trend Interpretation
PCB 28	−9.0 × 10−5	0.0408	0.996	Significant decreasing trend
PCB 52	−4.5 × 10−5	0.3333	0.75	No significant change
PCB 101	−1.0 × 10−5	0.9521	0.005	No discernible trend
PCB 138	−1.2 × 10−4	0.4932	0.511	Moderate, non-significant decline
PCB 153	−2.5 × 10−4	0.1163	0.967	Strong trend, not statistically significant
PCB 180	−2.8 × 10−4	0.30244	0.791	Persistent but declining
Ʃ6PCBs	−4.7 × 10−4	0.37826	0.687	Statistically insignificant overall decrease

).

Among the congeners, PCB 28 demonstrated a statistically significant decreasing trend (p = 0.04, R² = 0.996), suggesting efficient environmental degradation or effective source removal. While PCB 52 and PCB 180 showed downward trends, their changes were not statistically significant, indicating possible residual sources or slower degradation kinetics. PCB 101 revealed no significant trend (p = 0.95), with variations likely attributable to site-specific or episodic contamination. Notably, total PCB levels (Σ6PCBs) also decreased, supporting the effectiveness of implemented regulatory and environmental control measures.

These results confirm a general downward trend in PCB contamination across Bucharest. However, the persistence of higher-chlorinated congeners, particularly PCB 180, emphasizes the need for targeted monitoring and remediation in areas where these compounds remain prevalent.

3.3.2. Kruskal–Wallis Analysis

To complement the regression analysis and account for small sample size and non-normal data distributions of PCB concentration data, a Kruskal–Wallis statistical analysis was applied to evaluate temporal differences in individual PCB congeners and the total Σ6PCB across the three sampling years (2002, 2012, 2022). This non-parametric statistical method is appropriate for environmental datasets with limited replicates and helps determine whether observed changes are statistically significant or due to random variation.

The results reveal that PCB 28 (p = 0.04) and Σ6PCB (p = 0.02) exhibit statistically significant differences (p < 0.05) over time, indicating a true decline in concentrations rather than natural fluctuations. These findings support the hypothesis that environmental regulations, reduced industrial activity, and natural degradation processes have contributed to the observed reductions.

In contrast, other congeners, including PCB 52, PCB 101, PCB 138, PCB 153, and PCB 180, showed no statistically significant change (p > 0.05), though some displayed declining trends. These results may reflect the persistent nature of higher-chlorinated congeners or ongoing localized contamination sources, particularly for PCB 180, which remains elevated in specific areas.

These results confirm that observed trends, particularly for PCB 28 and total PCBs, reflect genuine environmental improvement rather than sampling variability (Figure 6).

3.4. Spatial Analysis of PCB Distribution

Spatial modeling of PCB concentrations was performed using Inverse Distance Weighting (IDW) interpolation to generate contamination maps for the years 2002, 2012, and 2022 (Figure 7). These maps reveal the temporal evolution and spatial distribution of PCB contamination across Bucharest. In 2002, PCB hotspots were primarily located in industrial zones and along major traffic corridors, reflecting legacy emissions from manufacturing and vehicular sources. By 2012, certain industrial sites showed declining concentrations, yet shifts in contamination patterns suggested influences from urban runoff and atmospheric deposition, dispersing pollutants to new areas. By 2022, overall PCB levels had decreased substantially, aligning with the broader trend of contamination reduction observed across the study. However, several localized hotspots persisted, particularly near former industrial complexes and high-traffic roadsides. Notably, sites such as P29, P30, and P40 continued to exhibit elevated levels of PCB 180, likely due to ongoing vehicle emissions and dust resuspension. In addition, urban green spaces near industrial zones, including P36 and P39, showed accumulated contamination over time, suggesting passive deposition in areas perceived as low risk. This underscores the importance of continued monitoring and targeted remediation in areas with persistent elevated levels.

IDW was chosen for its computational simplicity, ease of interpretation, and suitability for visualizing spatial patterns in environmental studies, especially when the sampling network is not uniform. However, several limitations must be considered. First, IDW interpolation does not incorporate spatial autocorrelation, which can limit its ability to capture broader geostatistical patterns. Second, results are highly sensitive to the selection of the power parameter—lower values can overly smooth variations, while higher values can exaggerate localized anomalies. Lastly, edge effects are a common limitation in IDW, where predictions at the borders of the study area may lack accuracy due to fewer neighboring data points. Despite these drawbacks, IDW remains a robust and practical tool for preliminary spatial analysis in urban soil contamination assessments.

3.5. Health Risk Assessment Results

The health risk assessment results were derived by calculating site-specific exposure doses for each of the 13 sampling locations based on the average concentrations of PCB congeners in 2022. Risk values were computed separately for adults and children using the pathway-specific exposure parameters presented in Table 2. The final values presented in Table S2 represent the average results across all sampling sites, grouped by age category and exposure route. These results indicate that both children and adults are well within safe exposure thresholds for PCBs in Bucharest’s urban soils.

For non-carcinogenic risk, the hazard index (HI) was calculated to be 0.01020 for adults and slightly higher at 0.01946 for children—both well below the threshold of 1, which represents the limit of acceptable chronic exposure. Among the exposure routes, ingestion contributed most to the total HQ values, followed by dermal contact, while inhalation was a negligible route.

Regarding carcinogenic risk, the total lifetime cancer risk (RISK_T) was estimated at 2.98 × 10⁻⁸ for adults and 6.25 × 10⁻⁸ for children, both of which are significantly lower than the U.S. EPA’s regulatory threshold of 1 × 10⁻⁶. These results suggest that the potential for developing cancer from current soil PCB exposure is negligible for both demographic groups.

As expected, children exhibit higher relative risk due to their lower body weight, higher soil ingestion rates, and greater dermal surface area-to-body weight ratios. These physiological and behavioral differences underline the importance of age-specific exposure assessments in environmental health evaluations. Overall, the findings affirm that current PCB concentrations in Bucharest’s urban soils do not pose a significant health threat under the assessed exposure conditions. Nonetheless, localized contamination hotspots still warrant targeted remediation and continued monitoring, particularly to protect vulnerable populations (

Table 5. Summary of non-carcinogenic (hazard index) and carcinogenic (total cancer risk) health risks for adults and children based on PCB exposure in urban soils of Bucharest.

Group	HI (Non-Carcinogenic Risk)	RISKT (Total Cancer Risk)
Adults	0.01020	2.98 × 10−8
Children	0.01946	6.25 × 10−8

).

While the health risk assessment indicates that both non-carcinogenic and carcinogenic risks from PCB exposure in Bucharest’s urban soils remain well below regulatory concern thresholds, it is important to acknowledge certain uncertainties inherent to the methodology. Key assumptions include standardized exposure frequency (EF), soil ingestion rates (IngR), and dermal contact parameters, which may not capture individual variability, especially among sensitive subgroups, such as children. For instance, child-specific behaviors—such as increased hand-to-mouth activity, greater time spent outdoors, and proximity to soil surfaces—may lead to higher actual exposure than estimated. Additionally, the assumption of uniform exposure across sites and over time may not fully reflect the heterogeneity of environmental conditions and pollutant distributions. These uncertainties suggest that while current risk levels appear negligible, precautionary monitoring should continue, particularly in known hotspots or areas with high human activity.

4. Discussion

This study presents a two-decade evaluation of polychlorinated biphenyl contamination in Bucharest’s urban soils, reflecting persistent legacy pollution. The consistent decline in total PCB concentrations (Σ6PCBs) from 2002 to 2022, confirmed by regression and Kruskal–Wallis analyses, underscores the effectiveness of regulatory interventions, such as the Stockholm Convention and national legislation, MO 756/1997.

Despite this positive trend, congener-specific behavior reveals complexities. While low-chlorinated PCBs (e.g., PCB 28) show significant reductions—probably due to volatilization or degradation—higher-chlorinated congeners, in particular PCB 180, remain persistent in the environment and dominant in the congener profile. Their recalcitrance is attributed to strong soil sorption and resistance to natural attenuation processes.

Over the past two decades, the sources of PCB contamination in Bucharest have evolved significantly. In the early 2000s, contamination was primarily associated with legacy sources, including former industrial platforms, electrical transformer stations, and poorly managed landfills containing PCB-laden materials. These sources were responsible for the high concentrations observed during the 2002 and 2012 campaigns, particularly in sites adjacent to decommissioned industrial areas. However, the observed decline in total PCB concentrations and the changing congener profile—most notably the disappearance of PCB 28 and the persistence of PCB 180—suggest a shift toward secondary sources. These include the remobilization of previously deposited PCBs through atmospheric deposition, resuspension of contaminated roadside dust, and surface runoff, particularly in high-traffic corridors, such as Kiseleff and Băneasa. The persistence of PCB 180, a hepta-chlorinated and highly sorptive congener, points to ongoing low-level inputs from diffuse sources, such as wear from building materials, deteriorated insulation, or combustion-related processes. Additionally, spatial patterns indicate that traffic-related activities may now play a more prominent role in sustaining residual contamination, especially in areas where soil disturbance and dust generation are common. This shift from direct industrial discharge to diffuse urban remobilization mechanisms aligns with broader trends reported in other post-industrial urban environments [28,77]. It also supports the need for ongoing monitoring and potentially targeted remediation efforts, particularly in traffic-dense and historically contaminated zones.

The decline in Σ6PCB concentrations observed between 2002 and 2022 reflects the cumulative effects of regulatory enforcement, improved waste handling, and the progressive elimination of primary PCB sources. However, the persistence of certain congeners, particularly PCB 180, in specific hotspots suggests that secondary dispersion mechanisms, such as atmospheric deposition, soil-to-air exchange, and vehicular dust resuspension, continue to redistribute PCBs within the urban environment. These processes do not drive the overall decrease but may affect how and where PCBs persist, possibly slowing the rate of decline in certain locations or altering spatial patterns over time. Understanding this distinction is essential for designing effective long-term monitoring and remediation strategies.

Spatial analysis using IDW interpolation shows that while PCB hotspots have decreased overall, residual contamination persists in former industrial areas and high-traffic corridors, particularly in areas such as P29 and P30. These observations suggest that secondary dispersion mechanisms—such as atmospheric deposition and resuspension of vehicle dust—continue to redistribute PCBs across the urban landscape, affecting areas once considered low risk. Although the IDW method effectively revealed temporal and spatial patterns, the limited number and uneven distribution of sampling points—particularly in the eastern and southern sectors—introduce a degree of uncertainty into the interpolated surfaces. While this limitation does not undermine the general trends observed, it highlights the need for a denser sampling network in future investigations to strengthen spatial resolution and improve risk assessment.

The health risk assessment corroborates a reassuring outcome: carcinogenic and non-carcinogenic risks remain well below USEPA thresholds for both adults and children. However, the relatively higher values observed for children underscore the need for vulnerability-specific strategies in public health risk management.

When contextualized alongside international studies, Bucharest’s case aligns with broader global trends in POP reduction. A recent study conducted in rural Transylvanian communities [78] reported low PCB levels in upper soils and negligible cancer risks, despite differences in population density, land use, and socioeconomic conditions. This consistency across divergent settings highlights the widespread decline of legacy PCB contamination in Romania, regardless of urban or rural context. International comparisons further support these conclusions. For example, investigations in China by Xu et al. (2018) [72] and Zhang et al. (2023) [74] identified comparable concentrations of persistent organic pollutants (POPs), including PCBs, in contaminated rural and agricultural soils. These studies also reported cancer risk values ranging between 10⁻⁸ and 10⁻⁵, aligning closely with the negligible risk levels observed in Bucharest. Similar outcomes were documented in Pakistan (Sultan et al., 2019) [79] and Nigeria (Adesina et al., 2023) [65], where soil samples from industrial and university environments exhibited low to moderate PCB presence, yet maintained cancer risk estimates below regulatory concern levels.

To place Bucharest’s PCB soil contamination into a broader Eastern and Central European context, comparative studies from several countries highlight the persistence of these pollutants due to varying historical uses and management practices. For example, in Estonia, soil samples from Tallinn showed concentrations up to 0.012 mg/kg dry weight, indicating localized contamination [80]. In Croatia, soils near the Plomin coal-fired power plant were significantly burdened by PCBs, and when compared to an urban-industrialized area like Varaždin, it was evident that industrial activities are major contributors to PCB presence in soil [81]. A particularly severe case occurred in Kragujevac, Serbia, following the 1999 NATO bombing of industrial facilities. PCB levels in soil samples around the Zastava car factory reached 70–74 mg/kg, with associated toxic dioxins (PCDD/Fs) as high as 10.2 mg/kg I-TEQ, even after cleanup efforts [82]. These findings confirmed both vertical and horizontal migration of PCBs within the soil, with significant bioactivity observed in vivo tests. In Bratsk, Russia, PCB contamination was attributed to outdated electrical infrastructure and industrial emissions from energy-intensive industries and wood processing plants. Soil PCB concentrations in urban environments were found to be significantly elevated, emphasizing the legacy impact of Soviet-era industrial practices [83]. In Germany, the situation remains complex. Historical use of PCBs in both closed (transformers, capacitors) and open (sealants, paints) applications has led to continued environmental contamination. As of 2013, over 12,000 tonnes of PCBs were estimated to remain in open applications, releasing 7–12 tonnes annually into the environment. Soil levels of 5 ng PCB-TEQ/kg (equivalent to 0.000005 mg/kg) have been linked to exceedances of EU safety thresholds in beef and chicken, highlighting the food chain risks associated with even low-level contamination [84].

These examples illustrate the persistent nature of PCB contamination across Europe and reinforce the importance of long-term monitoring, effective source identification, and risk-based remediation—principles that also underpin the present study in Bucharest.

While this study provides a comprehensive view of PCB contamination in surface soils, it is important to acknowledge that POPs such as PCBs can migrate into deeper soil layers and groundwater systems or be transported via surface runoff into urban water bodies, where they may accumulate in bottom sediments. Due to their hydrophobicity and strong affinity for organic matter, PCBs tend to adsorb to particles and settle in sediments, where they can persist for decades [85]. Sediments, in turn, can act as secondary sources, releasing PCBs under changing redox conditions or during storm events [86]. Future research should therefore integrate multi-compartment assessments—including soil, groundwater, and sediment—especially in historically industrial and densely urbanized environments, such as Bucharest.

Based on the spatial and temporal findings of this study, several key actions can be proposed to support evidence-based environmental management in Bucharest. First, targeted remediation should prioritize persistent PCB 180 hotspots, such as sites P29 and P30, where concentrations have consistently exceeded warning or intervention thresholds. Soil washing, stabilization, or bioremediation may be viable techniques depending on site conditions. Second, urban planning authorities should consider implementing stricter controls on vehicular emissions and dust resuspension near contaminated corridors, as traffic-related dispersion appears to contribute to persistent contamination. Finally, long-term monitoring programs should be institutionalized, particularly in green spaces adjacent to historical industrial zones, to prevent passive exposure accumulation. These strategies would help maintain the declining trend in PCB concentrations while addressing the localized risks posed by persistent hotspots.

While the findings of this study provide valuable insights into the temporal and spatial dynamics of PCB contamination in Bucharest’s urban soils, several limitations should be acknowledged. First, the sample size of 13 monitoring sites, although selected for their historical relevance and representativeness, remains relatively limited for a city the size of Bucharest. This may restrict the generalizability of the results. Second, potential unaccounted sources of PCB emissions, such as recent urban development projects, undocumented waste disposal, or materials from renovated buildings, could have influenced the contamination levels but were not explicitly addressed. Lastly, although the analytical procedures followed U.S. EPA method 8082A and employed certified reference materials, the detection limits of the instrumentation may still pose constraints in identifying ultra-trace concentrations, particularly for congeners with lower environmental mobility. Future studies should aim to expand the spatial coverage and incorporate multi-media assessments (e.g., dust, water, biota) to capture a more comprehensive picture of exposure and risk.

Across these global contexts, a common pattern emerges: trace levels of PCBs persist due to historical industrial activities, although contemporary exposure scenarios rarely exceed health risk thresholds. Future strategies should integrate targeted soil remediation, improved waste management and routine monitoring tailored to site-specific conditions.

5. Conclusions

This study provides a longitudinal assessment of polychlorinated biphenyl contamination in Bucharest’s urban soils over a 20-year span, from 2002 to 2022. The results demonstrate a notable reduction in total PCB concentrations (Σ6PCBs), decreasing from 0.0159 mg/kg in 2002 to 0.0065 mg/kg in 2022. This downward trend reflects the cumulative impact of regulatory enforcement, reduced industrial activity, improved waste management, and the natural attenuation of contaminants in urban soils.

Although overall contamination levels have declined, persistent hotspots remain, particularly in areas with a history of industrial use or high traffic exposure. PCB 180 continues to dominate the congener profile due to its chemical stability and resistance to degradation, highlighting the challenges of managing higher-chlorinated congeners. These findings underscore the importance of maintaining congener-specific monitoring and prioritizing remediation in vulnerable locations, such as P29 and P30.

The health risk assessment confirms that current soil PCB concentrations pose negligible carcinogenic and non-carcinogenic risks for both adults and children. Nonetheless, children exhibit relatively higher vulnerability due to physiological and behavioral factors, suggesting the need for age-specific consideration in future risk management.

Spatial modeling reinforces these conclusions, showing a reduction in contamination across the city but also identifying residual hotspots that require targeted attention. Continued environmental monitoring, focused soil remediation efforts, and adherence to national standards, such as MO 756/1997, are essential for sustaining progress in pollutant reduction and protecting public health.

This study presents the first city-wide, multi-decade assessment of PCB contamination in Bucharest’s urban soils, offering valuable insights into the persistence and spatial behavior of six major PCB congeners. By integrating field sampling, spatial interpolation, and risk assessment, it provides evidence of declining PCB trends over time while identifying areas requiring targeted monitoring. The outcomes not only support the effectiveness of past environmental regulations but also offer a replicable framework for assessing legacy pollutants in other rapidly urbanizing post-industrial regions.