Characteristics, Sources, and Risk Assessment of Polycyclic Aromatic Hydrocarbons in Soils and Sediments in the Yellow River Delta, China

Abstract

This study investigates the presence, origin, and associated ecological and human health risks of polycyclic aromatic hydrocarbons (PAHs) in soils from uncultivated lands and beach sediments within the Yellow River Delta (YRD), China. The measured concentrations of 16 priority PAHs in soils spanned 24.97–326.42 ng/g (mean: 130.88 ng/g), while concentrations in sediments ranged from 46.17 to 794.32 ng/g, averaging 227.22 ng/g. In terms of composition, low-molecular-weight PAHs predominated in soil samples, whereas high-molecular-weight compounds were more prevalent in sediments. The positive matrix factorization (PMF) model results suggested that petroleum pollution and fuel combustion were the main sources of PAHs in soils, whereas the contribution in sediments was derived from petroleum and traffic pollution. The ecological risk assessment results indicated that there existed no obvious ecological risk of soil PAHs, but sediment PAHs could negatively impact the surrounding ecological environment, especially in the northern coastal beach area. In addition, soil PAHs posed no potential carcinogenic risk to humans. Further pollution prevention and management measures are required in this region to ensure the safety of the environment.

1. Introduction

Polycyclic aromatic hydrocarbons (PAHs) are a group of long-lasting organic contaminants found broadly across air, soil, water, and sediments. These compounds consist of structures with two to seven fused aromatic rings, which may be organized in linear, angular, or compact configurations [1]. PAHs have become the focus of attention because these substances are numerous and widely distributed and cause great harm to human health and the ecological environment. PAHs exhibit notable carcinogenic, teratogenic, and mutagenic characteristics and phototoxic effects [2]. Under the effect of long-distance transmission, pollution can be expanded from the regional scale to the global scale [3]. Moreover, PAHs can be bioaccumulated and transmitted through the food chain, thus increasing the degree of risk [4]. In the natural environment, PAHs are predominantly retained in soils and sediments, with soils in particular harboring over 90% of the total PAH burden. In recent years, significant methodological advances have been made in the monitoring and risk assessment of PAHs. Passive sampling approaches, particularly those utilizing polydimethylsiloxane (PDMS)-based media, have proven effective in capturing time-weighted concentrations of freely dissolved and bioavailable PAHs, thus improving environmental representativeness compared to conventional grab sampling techniques [5]. Moreover, the integration of machine learning algorithms into health risk modeling frameworks has enhanced the predictive accuracy of PAH bioaccessibility and exposure outcomes, offering valuable support for risk-based site prioritization and management decisions [6]. Therefore, PAH pollution represents an important part of environmental monitoring in most countries, and many studies have investigated the pollution characteristics, potential sources, and environmental risks of PAHs.

The Yellow River Delta (YRD) was mainly formed via the combined action of marine dynamics and sediment impact of Yellow River runoff, which occupies a major position in global wetland ecosystems. The Yellow River Delta’s coastal wetlands host diverse rare flora and fauna and serve as key breeding and migratory sites for endangered bird species across Northeast Asia and the Western Pacific region. Underground, the YRD contains abundant petroleum- and gas-based mineral resources, and it is an important energy base and hosts the second largest Shengli Oilfield in China. Since the 1960s, petroleum field exploration and exploitation activities have directly promoted rapid economic development of the region. The Yellow River Delta also serves as a significant base for agricultural and fishery activities. Its development has been instrumental in advancing regional growth around Bohai Bay.

Intensive exploitation of hydrocarbon resources, coupled with industrial and construction-related human activities, has led to a noticeable increase in pollutant emissions, posing significant threats to the region’s ecological integrity [7], such as a reduction in the wetland area, water eutrophication, and a diversity decrease. Both the ocean and land are polluted and damaged to varying degrees [8,9], in which the petroleum pollution problem is particularly prominent and has attracted extensive attention. Previous studies in this area mostly focused on coastal wetlands or the Yellow River estuary; until now, few studies have been conducted considering the PAH distribution on a regional scale, especially involving uncultivated land soil. The YRD exhibits a very large scale of uncultivated land and is the area with the most land reserve resources in the eastern coastal area of China. Abundant land resources can not only provide suitable conditions for local development of ecological, efficient, and sustainable industries but can also promote the potential of economic and social development. Therefore, it is of great practical significance to study uncultivated land pollution. Accordingly, this study aimed to assess the levels and composition of PAHs in soils and sediments, trace their likely sources, and analyze the related ecological and human health risks. The findings are intended to inform environmental management strategies and support restoration planning in the Yellow River Delta.

2. Materials and Methods

2.1. Study Area

The Yellow River Delta (YRD), situated in eastern China between 118°07′–119°18′ E and 36°55′–38°12′ N, lies predominantly within Dongying City, Shandong Province, which encompasses about 96% of the region. The study area spans approximately 2152.7 km² and includes Xianhe, Gudao, and Huanghekou towns. Climatically, the region is shaped by both the Eurasian landmass and the Western Pacific, resulting in a warm temperate semi-humid continental monsoon climate. Average annual temperatures range between 11.7 °C and 12.8 °C, with yearly precipitation totaling around 530–630 mm, over half of which occurs in summer. The region is rich in natural resources, including petroleum, brine, natural gas, minerals, and geothermal energy. Proven petroleum reserves reach 5.4 billion tons, accompanied by roughly 230 billion cubic meters of natural gas.

2.2. Sample Collection

In July 2021, surface soil (n = 32) and coastal sediment (n = 6) samples were collected from the Yellow River Delta region. Sampling sites were selected using a grid method with a spacing of 6 km × 6 km to ensure spatial coverage. To minimize anthropogenic interference, sites were deliberately located in areas distant from roads, residential zones, industrial facilities, and cultivated land, based on satellite imagery and field observations. At each site, three replicates were collected to ensure representativeness. Surface soil samples were obtained from the 0–20 cm layer using decontaminated stainless steel shovels and hand augers to avoid cross-contamination. Coordinates for all sampling locations were recorded using a handheld GPS receiver (Figure 1). After removing surface debris such as stones and plant roots, composite samples were thoroughly homogenized and subsampled using the quartering method. Approximately 1 kg of each homogenized sample was sealed in opaque polyethylene Ziplock bags. Immediately after collection, all samples were placed in coolers with ice packs and transported to the laboratory. They were subsequently stored at −20 °C under dark conditions prior to analysis to minimize degradation of organic pollutants.

2.3. Sample Extraction, Analysis, and Quality Control

A 10 g portion of each dried and homogenized sample underwent Soxhlet extraction using 200 mL of an acetone and n-hexane mixture (1:1, v/v) over a period of 16 to 18 h, maintaining a reflux frequency of 4–6 cycles per hour. The resulting extract was concentrated to ~2 mL via rotary evaporation, followed by purification through a silica gel chromatography column (10 mm × 300 mm). Elution was carried out using 25 mL of a dichloromethane and pentane solution (1:1, v/v). The collected eluent was further concentrated and adjusted to a final volume of 1 mL with the same acetone/n-hexane mixture for subsequent instrumental analysis. All samples were processed in duplicate to confirm analytical consistency.

Sixteen priority PAHs, as designated by the United States Environmental Protection Agency (USEPA), were identified in accordance with the gas chromatography–mass spectrometry (GC–MS) method outlined in HJ 805-2016 [10]. These compounds included naphthalene (Nap), acenaphthylene (Acpy), acenaphthene (Ace), fluorene (Flu), phenanthrene (Phe), anthracene (Ant), fluoranthene (Fla), pyrene (Pyr), benzo[a]anthracene (BaA), benzo[b]fluoranthene (BbF), benzo[k]fluoranthene (BkF), benzo[a]pyrene (BaP), indeno[1,2,3-cd]pyrene (IcdP), dibenzo[a,h]anthracene (DahA), and benzo[ghi]perylene (BghiP). The analysis was conducted using a GC–MS system (Agilent 6890N GC coupled with a 5975B MS detector, Santa Clara, CA, USA) equipped with a DB-5 MS capillary column (30 m × 0.25 mm i.d., film thickness: 0.25 μm), with helium serving as the carrier gas. The temperature program was initiated at 80 °C (held for 2 min), ramped to 180 °C at 20 °C/min and held for 5 min, and then further increased to 290 °C at 10 °C/min, with a final hold of 5 min.

To guarantee data precision and reliability, rigorous quality control measures were implemented during all stages of analysis. Quality assurance included blank samples, matrix spiking, and duplicate analyses. A blank was processed for every batch of 20 samples, while all duplicate samples exhibited relative standard deviations below 20%. Recovery rates for the 16 PAHs in spiked samples ranged between 40% and 150%, which fell within acceptable limits. Quantification was conducted using the external standard method, employing a certified 16-PAH standard mixture. All calibration curves exhibited correlation coefficients exceeding 0.995. The detection limits (LODs) ranged from 0.08 to 0.17 ng/g, while quantification limits (LOQs) ranged between 0.32 and 0.68 ng/g.

2.4. Ecological Risk Assessment

2.4.1. Toxicity Equivalent Quotient (TEQ)

The toxicity equivalent quotients of the above PAHs relative to BaP (TEQ_BaP) were used in ecological risk assessment [11]. BaP was assigned a toxic equivalency factor (TEF) of 1, while the remaining PAHs were given respective TEF values based on their relative toxicities, as detailed in

Table 1. Toxicity equivalent factors of the individual PAHs.

Individual PAHs	Ring Numbers	TEF	Individual PAHs	Ring Numbers	TEF
Nap	2	0.001	Pyr	4	0.001
Ant	3	0.01	Fla	4	0.001
Phe	3	0.001	DahA	5	1
Flu	3	0.001	BaP	5	1
Ace	3	0.001	BkF	5	0.1
Acpy	3	0.001	BbF	5	0.1
Chr	4	0.01	BghiP	6	0.01
BaA	4	0.1	IcdP	6	0.1

. The calculation equation is as follows:

$${\mathrm{TEQ}}_{\mathrm{BaP}}=\sum {\mathrm{C}}_{\mathrm{i}}\times {\mathrm{TEF}}_{\mathrm{i}}$$

(1)

where C_i is the concentration of the individual PAHs and TEF_i is the equivalent toxicity factor of the individual PAHs. The higher the TEF of the individual PAH is, the higher the toxicity.

2.4.2. Effect Range Low/Effect Range Median (ERL/ERM)

The ecological risk assessment framework developed by Long et al. [12] has been widely applied to evaluate the potential hazards of PAHs in environmental media [13,14]. This method uses two threshold values—effect range low (ERL) and effect range median (ERM)—to classify risk levels. Based on this approach, environmental quality can be categorized into three ecological risk grades according to PAH concentrations: rarely contaminated (<ERL), occasionally contaminated (≥ERL and <ERM), and frequently contaminated (≥ERM).

2.5. Health Risk Assessment

Incremental Lifetime Cancer Risk (ILCR)

The incremental lifetime cancer risk (ILCR) model was employed to quantitatively assess the carcinogenic risk associated with PAHs in soils, representing the estimated probability of cancer development from long-term exposure to specific doses of carcinogens. Human exposure to soil-bound PAHs primarily occurs through three pathways: direct ingestion (ILCR_ingestion), inhalation of airborne particles (ILCR_inhalation), and dermal contact with contaminated soil (ILCR_dermal) [15]. The calculation equation of the carcinogenic risk under each pathway is as follows:

$$\mathrm{CS}=\sum \left({\mathrm{PAH}}_{\mathrm{i}}\times {\mathrm{TEF}}_{\mathrm{i}}\right)$$

(2)

$${\mathrm{ILCR}}_{\mathrm{ingestion}}=\mathrm{CS}\times \left({\mathrm{CSF}}_{\mathrm{ingestion}}\times \sqrt[3]{{\displaystyle \frac{\mathrm{BW}}{70}}}\right)\times {\mathrm{IR}}_{\mathrm{soil}}\times \mathrm{EF}\times \mathrm{ED}/\mathrm{BW}\times \mathrm{AT}\times {10}^6$$

(3)

$${\mathrm{ILCR}}_{\mathrm{inhalation}}=\mathrm{CS}\times \left({\mathrm{CSF}}_{\mathrm{inhalation}}\times \sqrt[3]{{\displaystyle \frac{\mathrm{BW}}{70}}}\right)\times {\mathrm{IR}}_{\mathrm{air}}\times \mathrm{EF}\times \mathrm{ED}/\mathrm{BW}\times \mathrm{AT}\times \mathrm{PEF}$$

(4)

$${\mathrm{ILCR}}_{\mathrm{dermal}}=\mathrm{CS}\times \left({\mathrm{CSF}}_{\mathrm{dermal}}\times \sqrt[3]{{\displaystyle \frac{\mathrm{BW}}{70}}}\right)\times \mathrm{SA}\times \mathrm{AF}\times \mathrm{ABS}\times \mathrm{EF}\times \mathrm{ED}/\mathrm{BW}\times \mathrm{AT}\times {10}^6$$

(5)

$${\mathrm{ILCR}}_{\mathrm{s}}={\mathrm{ILCR}}_{\mathrm{ingestion}}+{\mathrm{ILCR}}_{\mathrm{inhalation}}+{\mathrm{ILCR}}_{\mathrm{dermal}}$$

(6)

where CS is the toxic equivalent concentration of PAHs (mg/kg) [16], PAH_i is the concentration of the individual PAHs, TEF_i is the toxic equivalent factor of the individual PAHs (Table 1), and CSF is the carcinogenic slope factor (mg/(kg·day)), which can be determined based on the carcinogenic ability of BaP. The values of CSF_ingestion, CSF_inhalation, and CSF_dermal were 7.3, 3.85, and 25, respectively. Exposure parameters were defined separately for adults and children to reflect physiological and behavioral differences, with children assumed to have lower body weight but higher ingestion and dermal contact potential per unit body mass, as shown in

Table 2. Parameters used in the incremental lifetime cancer risk method.

Parameter	Description	Unit	Adult	Children
BW	Body weight	kg	61.5	15
IRsoil	Soil ingestion rate	mg/day	100	200
EF	Exposure frequency	days/a	350	350
ED	Exposure time	years	24	6
AT	Average life span	days	25,550	25,550
IRair	Inhalation rate	m3/day	20	10
PEF	Soil particle emission factor	m3/kg	1.36 × 109	1.36 × 109
SA	Dermal exposure area	cm2/day	5700	2800
AF	Dermal adhesion factor	mg/cm2	0.07	0.2
ABS	Dermal absorption parameter	unitless	0.13	0.13

. ILCR_s is the sum of the carcinogenic risks under the three exposure pathways. For ILCR_s < 10⁻⁶, the carcinogenic risk is considered negligible; for ILCR_s > 10⁻⁴, the carcinogenic risk is high; and for ILCR_s values between 10⁻⁶ and 10⁻⁴, a potential carcinogenic risk exists.

2.6. Statistical Analysis

To trace the potential origins of PAHs in both soils and sediments, the positive matrix factorization (PMF) model was applied using the EPA PMF 5.0 software. Spatial distribution patterns of PAHs were visualized through kriging interpolation. Data organization was carried out in Excel 2010, while graphical outputs were generated using Origin 8.5.

3. Results and Discussion

3.1. PAH Concentration

3.1.1. PAH Concentrations in Uncultivated Land Soil in the YRD

Table 3. Descriptive statistics of the PAHs in the soils (ng/g).

PAHs	Range	Mean	SD	CV	Detection Rate (%)
Nap	ND~228.29	100.89	53.39	0.53	96.88
Ant	ND~48.36	2.23	8.74	3.93	9.38
Phe	ND~48.36	2.60	8.89	3.42	12.5
Flu	ND~9.44	2.34	3.76	1.61	28.13
Ace	ND	ND	ND	ND	ND
Acpy	ND	ND	ND	ND	ND
Chr	ND~32.92	2.20	7.26	3.31	9.38
BaA	ND~43.90	4.27	10.98	2.57	15.63
Pyr	ND~24.18	3.92	6.23	1.59	31.25
Fla	ND~13.14	5.44	5.82	1.07	46.88
DahA	ND	ND	ND	ND	ND
BaP	ND~13.75	5.66	5.71	1.01	50.00
BkF	ND	ND	ND	ND	ND
BbF	ND	ND	ND	ND	ND
BghiP	ND	ND	ND	ND	ND
IcdP	ND~11.52	1.34	3.56	2.65	12.50
ΣPAH7	ND~98.76	13.47	22.32	1.66	53.13
ΣPAH16	24.97~326.42	130.88	65.12	0.50	100.00

Notes: ND: not detected; SD: standard deviation; ΣPAH₇: concentrations of 7 carcinogenic PAHs (BaA, Chr, BbF, BkF, BaP, IcdP, and DahA); ΣPAH₁₆: total concentrations of the 16 PAHs; the same applies below.

presents the concentrations of all sixteen target PAHs, including seven classified as carcinogenic, in the soil samples from the YRD. Most PAHs were detected to varying extents, with detection frequencies ranging between 9.38% and 96.88%, except for Ace, Acpy, DahA, BkF, BbF, and BghiP, which were not commonly observed. The detection rates of ΣPAH₇ and ΣPAH₁₆ were 53.13% and 100%, respectively. These findings indicate that soils across the study region were broadly influenced by PAH contamination. Chrysene (Chr) was identified in only 9.38% of the samples, reflecting its relatively low abundance in surface soils. The total concentrations of the 16 PAHs exhibited considerable variability, ranging from 24.97 to 326.42 ng/g, with a mean concentration of 130.88 ng/g. Site S26 exhibited the highest ΣPAH₁₆ concentration among all soil samples, likely due to emissions from nearby salt production facilities and intensive vehicular activity. In contrast, the lowest level of ΣPAH₁₆ was recorded at Site S20. There were no highly polluting enterprises or factories near this sampling site and few human activities, so the detected pollution was relatively low. As shown in

Table 4. Concentrations of the soil PAHs in different regions (ng/g).

Study Area	Types	Range	Mean	References
YRD (uncultivated land soil)	16	24.97~326.42	130.88	This study
YRD (farmland soil)	16	31.5~1399.4	149. 8	[17]
YRD (forest soil)	16	25.53~202.78	99.38	[18]
YRD (wetland soil)	16	70.58~1826.12	432.01	[19]
YRD (urban soil)	16	-	682.8	[20]
Pearl River Delta (wetland soil)	16	625.0~789.2	666.3	[21]
Liao River Delta (wetland soil)	16	106~3148	550	[22]
Beijing (urban soil)	16	ND~2730.1	210	[23]
Shanghai (urban soil)	16	227.85~16,461.75	3918.92	[24]
Zhengzhou (urban soil)	16	49.9~11,565	1567	[25]
Xi’an (farmland soil)	16	-	207	[26]
Guiyu (farmland soil)	16	56~567	-	[27]
Baise (mountain soil)	16	93.9~802.3	252.3	[28]
Yangtze River Delta (industrial soil)	19	16.3~4694	688	[29]
Pingshuo (industrial soil)	16	2160~33,520	11,940	[30]
Beijing (industrial soil)	16	ND~19,716.6	1006	[3]
Tianjin (industrial soil)	16	440~1360	988	[31]
Siberian (urban soil)	12	33.4~2495.3	356.2	[32]
Orlando (urban soil)	16	43~30,428	3227	[33]
Tampa (urban soil)	16	59~58,640	4562	[33]
Ma’an (traffic soil)	13	266.9~929.2	501	[34]
Ulsan (traffic soil)	16	310~1820	1079	[35]

, the PAH concentrations identified in this study were lower than those previously reported in wetland and urban soils of the region but slightly exceeded those found in forested areas. When compared with other cities, the study area exhibited relatively lower levels of PAH contamination. Analysis across various land use types revealed that PAH concentrations were markedly higher in industrial and traffic-related zones than in uncultivated land, farmland, or mountainous soils. This disparity underscores the significant influence of anthropogenic activities on environmental pollution. Without the implementation of effective and science-based control strategies, such pollution could pose a threat to the region’s ecological health.

The concentrations of the seven carcinogenic PAHs ranged from non-detectable (ND) to 98.76 ng/g, with an average of 13.47 ng/g, representing approximately 10% of the total ΣPAH₁₆. Among them, benzo[a]pyrene (BaP) exhibited the highest carcinogenic potential, with levels varying between ND and 13.75 ng/g and a mean value of 5.66 ng/g. Notably, naphthalene (Nap) had the highest average concentration among all 16 PAHs at 100.89 ng/g (Table 3), along with the highest detection frequency, likely due to petroleum industry activities in the area. To assess distribution variability, the coefficient of variation (CV) was calculated for each PAH. Based on standard classification [36], variability was grouped as low (CV < 10%), moderate (10% ≤ CV < 100%), and high (CV ≥ 100%). Table 3 shows that all PAHs, except Nap, exhibited high variability (CV ≥ 100%), with anthracene (Ant) displaying the greatest variation, suggesting greater sensitivity to external pollution sources. Soil PAH pollution levels were categorized according to the criteria by Maliszewska-Kordybach (1996) [37]: non-polluted (<200 ng/g), lightly polluted (200–600 ng/g), moderately polluted (600–1000 ng/g), and heavily polluted (>1000 ng/g). In this study, 87.5% of the sampling sites fell within the non-polluted category, while the remaining 12.5% were classified as lightly polluted.

3.1.2. PAH Concentrations in Coastal Beach Sediments near the Yellow River Estuary

The concentrations of 16 PAHs and 7 carcinogenic PAHs detected in coastal beach sediments near the Yellow River Estuary are shown in

Table 5. Descriptive statistics of the PAHs in the sediments (ng/g).

PAHs	Range	Mean	SD	CV	Detection Rate (%)
Nap	ND~155.27	71.39	63.28	0.89	83.33
Ant	ND~18.53	3.09	6.90	3.17	16.67
Phe	ND~18.53	3.09	6.90	2.24	16.67
Flu	ND~25.47	5.53	9.35	1.69	33.33
Ace	ND~9.26	1.54	3.45	3.17	16.67
Acpy	ND~9.26	1.54	3.45	3.17	16.67
Chr	ND~74.11	12.35	27.62	2.24	16.67
BaA	ND~92.63	22.62	33.19	1.47	50.00
Pyr	ND~55.58	14.73	19.83	1.35	50.00
Fla	ND~64.84	12.85	23.68	1.84	33.33
DahA	ND	ND	ND	ND	ND
BaP	ND~176	36.62	62.47	1.71	83.33
BkF	ND~64.84	10.81	24.17	2.24	16.67
BbF	ND~92.63	15.44	34.52	2.24	16.67
BghiP	ND~9.26	1.54	3.45	3.17	16.67
IcdP	ND~74.11	14.06	27.11	1.93	33.33
ΣPAH7	ND~574.32	111.90	207.43	1.85	83.33
ΣPAH16	46.17~794.32	227.22	262.55	1.16	100.00

Notes: ND: not detected; SD: standard deviation; ΣPAH₇: concentrations of 7 carcinogenic PAHs (BaA, Chr, BbF, BkF, BaP, IcdP, and DahA); ΣPAH₁₆: total concentrations of the 16 PAHs; CV: coefficient of variation.

. With the exception of DahA, all other PAHs were present to varying extents, with detection frequencies ranging from 16.67% to 83.33%. The detection rates for ΣPAH₇ and ΣPAH₁₆ were 83.33% and 100%, respectively, suggesting that PAH contamination is also prevalent in coastal sediments of the study area. The levels of ΣPAH₁₆ in sediment samples exhibited substantial variation, ranging from 46.17 to 794.32 ng/g, with an average of 227.22 ng/g. The highest concentration was observed at Site N5, which is likely influenced by offshore petroleum extraction activities. Conversely, the lowest ΣPAH₁₆ concentration was recorded at Site N6, an area with limited anthropogenic disturbance and located at a distance from major pollution sources. When compared to PAH levels in other bays along the Bohai Sea, the values reported here were higher than those in northern Liaodong Bay (89.9 ng/g) [38] but lower than those in southern Laizhou Bay (612.52 ng/g) [39]. This difference may reflect stronger oceanic transport influences on the PAH distribution in the current study region relative to in more inland bays. In comparison with domestic bay areas, PAH concentrations in these sediments were relatively low. However, when compared to petroleum-rich foreign coastal zones (

Table 6. Concentrations of the sediment PAHs in different regions (ng/g).

Study Area	Types	Range	Mean	References
Jiaozhou Bay	16	59.82~3979.55	965.18	[40]
Haizhou Bay	16	116.6~2414.9	662.42	[41]
Hangzhou Bay	16	32.1~171.1	-	[42]
Xinglin Bay	16	413.00~2748.81	949.56	[43]
Zhanjiang Bay	16	41.96~933.90	315.98	[23]
Leizhou Bay	16	21.72~319.61	103.91	[23]
Beibu Gulf	16	11.30~141.56	42.12	[44]
Chabahar Bay	16	0~93	-	[45]
Persian Gulf	16	10.33~186.16	103.87	[46]
Mexico Gulf	16	100~856	-	[47]
Bohai Bay	16	-	233.7	[48]

), the concentrations found in this study were comparatively elevated. These findings highlight the urgent need for strengthened pollution control and environmental protection efforts in coastal zones.

The concentrations of the seven carcinogenic PAHs in sediment samples ranged from non-detectable (ND) to 574.32 ng/g, with an average of 111.9 ng/g, representing 49.25% of the total ΣPAH₁₆. This proportion was approximately 8.3 times higher than that observed in the corresponding soil samples. Benzo[a]pyrene (BaP), recognized as the most carcinogenic PAH, exhibited concentrations between ND and 176 ng/g, with a mean value of 36.62 ng/g—6.5 times greater than its average in soils. Among all sedimentary PAHs, naphthalene (Nap) showed both the highest mean concentration (63.28 ng/g) and the highest detection frequency (83.33%). Coefficient of variation (CV) analysis indicated strong variability for most PAHs, excluding Nap. In particular, anthracene (Ant), acenaphthene (Ace), acenaphthylene (Acpy), and benzo[ghi]perylene (BghiP) were most sensitive to external pollution inputs over time (Table 5). The overall CV for ΣPAH₁₆ in sediments reached 116%, significantly exceeding the 50% recorded for soils, suggesting that sediment contamination levels were more heavily influenced by anthropogenic activities. In terms of pollution grading, most sediment sites fell within the non-polluted category. However, Site N5, located in the northern intertidal zone, showed moderate pollution, while Site N4 exhibited a light pollution level. Generally, sediment samples displayed greater PAH burdens than soils, particularly for carcinogenic PAHs and BaP, indicating the need for increased attention and management efforts in these areas.

3.2. Spatial Distribution of the PAHs

The concentration patterns of PAHs demonstrated evident spatial variability, with distinct localized pollution hotspots. Areas with elevated contamination were primarily located in Xianhe Town, northern Gudao Town, and northeastern Huanghekou Town of Dongying City, showing a gradual decline in levels moving away from these regions (Figure 2). The spatial trends of PAH distribution appear strongly influenced by regional industrial activities and resource exploitation. To the northeast of Xianhe Town lies the Dongying Port Economic Development Zone, where chemical manufacturing, equipment production, power generation, and logistics dominate the industrial landscape. Extensive use of fossil fuels in these industries can lead to the thermal breakdown and formation of PAHs. Additionally, petroleum handling and unloading activities at the port can result in oil-related pollution. In the northern coastal zone, petroleum extraction is actively conducted, contributing to elevated PAH concentrations in surrounding areas. Gudao Town, which centers around oil and gas exploration, faces environmental pressure from both operational leaks and pollutants such as wastewater, exhaust gases, and solid residues discharged by nearby chemical enterprises. Northeastern Huanghekou Town, situated along Provincial Road 315, is in proximity to two major oil production facilities in the Gudong region. The area also hosts popular tourist destinations along the Gudong seawall, with significant vehicular and human activity—factors that likely contribute to pollution from both petroleum and combustion sources. In contrast, the southern and eastern portions of Huanghekou Town encompass the Yellow River Delta Nature Reserve, characterized by limited infrastructure, absence of major transportation routes, and significant distance from petrochemical operations. Recent investments in ecological restoration and wetland conservation have likely contributed to its low pollution levels. It is important to acknowledge that sediment sampling in this study was limited (n = 6), which may restrict the accuracy of spatial interpretations. Therefore, the spatial distribution patterns of PAHs in sediments should be interpreted cautiously, and future research should include broader sampling coverage to enhance spatial resolution.

3.3. PAH Composition

3.3.1. PAH Composition in Uncultivated Land Soils in the YRD

Polycyclic aromatic hydrocarbons (PAHs) containing different numbers of aromatic rings are commonly used as indicators to infer their potential sources. Typically, low-molecular-weight PAHs (LMW; consisting of 2–3 rings) are primarily associated with oil spills or natural volatilization from fossil fuels, whereas high-molecular-weight PAHs (HMW; 4–6 rings) are largely generated through the incomplete combustion of petroleum products, biomass (such as grass and wood), coal, and vehicular emissions [49]. Thus, analyzing the compositional profile of PAHs offers important insights into source attribution.

Among the PAHs detected in soil samples, naphthalene (Nap) was dominant, comprising 77.09% of the total PAH concentration, followed by benzo[a]pyrene (BaP, 4.32%), fluoranthene (Fla, 4.16%), and benzo[a]anthracene (BaA, 3.26%). As illustrated in Figure 3a, the majority of PAHs in soils belonged to the 2-ring group (77.08%), followed by 4-ring (12.09%), 3-ring (5.47%), 5-ring (4.33%), and 6-ring (1.03%) compounds. Overall, LMW PAHs made up over 80% of the total PAHs detected. Nap alone contributed 93.37% to the LMW fraction, while BaP accounted for the largest share (24.81%) within the HMW group. Previous studies have noted that PAHs in soils can originate from both natural sources and anthropogenic activities [50]. Background concentrations attributed to natural processes—such as plant decay, wildfires, and volcanic emissions—typically fall within 1–10 ng/g. However, the PAH levels observed in this study substantially exceeded these baseline values, indicating significant influence from human activities in the region. Therefore, it can be inferred that PAHs in YRD soils originate not only from petroleum leakage but also from broader anthropogenic contributions. Additionally, due to their higher volatility [17], LMW PAHs are more easily mobilized via atmospheric transport, suggesting that long-range transmission may also play a role in soil PAH accumulation.

Figure 4a illustrates the distribution of PAHs by ring number at each soil sampling location. Across most sites, the PAH profiles were relatively consistent, with 2-ring compounds being the predominant species. At Sites S1, S11, S13, and S20, low-molecular-weight (LMW) PAHs accounted for the entire PAH content, suggesting recent contamination likely linked to petroleum leakage. In contrast, Sites S21 and S28 exhibited a notably higher proportion of high-molecular-weight (HMW) PAHs, particularly those with 4-ring structures. This pattern may be attributed to the proximity of these sites to oil extraction operations and chemical facilities, where activities such as fossil fuel combustion and elevated vehicular emissions can lead to increased HMW PAH deposition in soils.

3.3.2. PAH Composition in Coastal Beach Sediments near the Yellow River Estuary

As illustrated in Figure 3b, the distribution of PAHs by ring number in YRD sediments was in the following order: 2-ring (31.42%) > 5-ring (27.67%) > 4-ring (27.53%) > 6-ring (6.87%) > 3-ring (6.51%). This composition pattern indicates a predominance of high-molecular-weight (HMW) PAHs, which collectively made up 62.07% of the total ΣPAH₁₆. BaP attained the highest contribution (25.97%) to HMW PAHs, and the contribution of Nap was the highest (82.84%) to LMW PAHs. The concentration of the PAHs in the sediments at each sampling site also exceeded the typical endogenous pollution concentration, indicating that the coastal beach area was also affected by human factors. In contrast to the proportion of PAH rings in the sampled soils, the proportion of HMW PAHs in the sediments increased significantly. This part of the PAHs may stem from the exhaust gas and wastewater of factories and enterprises and the exhaust gas of port transportation and may enter seawater through atmospheric deposition, surface runoff, or other processes, finally accumulating in sediments. Therefore, the input of combustion sources may exert a greater impact on PAHs in the sediments in the YRD than that of petroleum sources.

The PAH ring number distribution at each sediment sampling site is shown in Figure 4b. At most sites, the proportion of LMW PAHs was larger than 50%, of which 2-ring PAHs comprised the majority, indicating the presence of petroleum PAH input. At Sites N1 and N5, HMW PAHs accounted for a larger proportion, revealing that fossil fuel combustion exhaust and vehicle exhaust emissions comprised the main sources of PAHs.

3.4. Source Apportionment

As illustrated in Figure 3b, the distribution of PAHs by ring number in YRD sediments was in the following order: 2-ring (31.42%) > 5-ring (27.67%) > 4-ring (27.53%) > 6-ring (6.87%) > 3-ring (6.51%). This composition pattern indicates a predominance of high-molecular-weight (HMW) PAHs, which collectively made up 62.07% of the total ΣPAH₁₆. Factor 1 exhibited a dominant loading of Pyr, which is widely regarded as an indicator of vehicular and industrial combustion processes [51], and was thus attributed to vehicular/industrial combustion. Factor 2 was characterized by a high contribution of BaP, a marker compound for gasoline vehicle emissions [52], and was therefore identified as traffic emissions. Factor 3 was dominated by Nap (94.19%), with additional contributions from IcdP, BaA, and Flu, indicating a mixed source of petroleum-related contamination and biomass combustion [53,54,55]. Factor 4 showed a strong loading of Fla, which is typically associated with coal combustion activities [56], and was accordingly identified as coal combustion (Figure 5). Based on the revised factor assignments, the relative contributions of each source to the total PAHs in soils were as follows: petroleum and biomass combustion (82.27%), vehicular/industrial combustion (8.49%), coal combustion (4.72%), and traffic emissions (4.52%) (Figure 6).

Figure 6 presents the source apportionment results for PAHs in both soil and sediment samples from the YRD, revealing contributions from both petroleum-related and combustion-derived origins. In soil samples, the dominant input came from petroleum pollution and general fuel combustion, accounting for 82.27% of the total PAHs. Additional contributions included fossil fuel combustion (8.49%), coal combustion (4.72%), and vehicular emissions (4.52%).

According to the above analysis, petroleum pollution, fossil fuel combustion, and traffic pollution were the main sources of PAHs in the study area, and biomass combustion sources accounted for a certain proportion. This may be associated with the development of petrochemical-related industries in this study area; a large number of petroleum reserves and corresponding petrochemical product processing production could cause PAH pollution. Moreover, the coast of the study area is located near the Dongying Port Economic Development Zone, so PAHs generated by boiler combustion, exhaust gas, and wastewater discharge from factories could be transmitted through atmospheric transmission, surface runoff, or other processes and could finally accumulate in soils and sediments. In addition, ship transportation and hydrocarbon exploitation activities in ports inevitably generate the risk of petroleum leakage. Furthermore, pollution stemming from other regions under the hydrodynamic conditions of the Yellow River Estuary is also a potential source of PAHs in the study area, so the contribution of petroleum pollution/combustion was high. Referring to Dongying’s annual statistical compilation, the annual consumption of coal fuel for industrial production has reached 11.25 million tons, crude oil consumption has reached approximately 55.48 million tons, natural gas consumption has reached 86,100 tons, and transportation fuel (gasoline and diesel) consumption has reached 75,800 tons. The large amount of combustion emissions of these substances is also an important factor that could result in PAH pollution. Moreover, the burning of firewood, straw, or other biomass sources used in the production and life activities of local residents is a pollution source that cannot be ignored. The PAHs produced could cause adverse effects on the environment.

3.5. Ecological Risk Assessment of the PAHs in the Soils and Sediments

3.5.1. Ecological Risk Results Based on TEQ

The toxicity equivalent concentrations (TEQs) of the 16 PAHs in YRD soil samples ranged between 0.02 and 16.86 ng/g, with an average of 6.38 ng/g. Notably, the seven carcinogenic PAHs contributed approximately 98% of the total TEQ, significantly exceeding the share of non-carcinogenic PAHs. This was primarily due to their elevated toxic equivalency factors. Among the carcinogenic PAHs, benzo[a]pyrene (BaP) exhibited the highest contribution to total TEQ, accounting for 88.71%, followed by benzo[a]anthracene (BaA) at 6.69%. Ecological risk was evaluated by comparing the calculated TEQ values to the Dutch soil remediation threshold of 33 ng/g. As shown in

Table 7. TEQ values of the soil and sediment PAHs.

PAHs	Soil			Sediment
	Minimum	Maximum	Mean	Minimum	Maximum	Mean
Nap	0.00	0.23	0.10	0.00	0.16	0.07
Ant	0.00	0.48	0.02	0.00	0.19	0.03
Phe	0.00	0.05	0.00	0.00	0.02	0.00
Flu	0.00	0.01	0.00	0.00	0.03	0.01
Ace	0.00	0.00	0.00	0.00	0.01	0.00
Acpy	0.00	0.00	0.00	0.00	0.01	0.00
Chr	0.00	0.33	0.02	0.00	0.74	0.12
BaA	0.00	4.39	0.43	0.00	9.26	2.26
Pyr	0.00	0.02	0.00	0.00	0.06	0.01
Fla	0.00	0.01	0.01	0.00	0.06	0.01
DahA	0.00	0.00	0.00	0.00	0.00	0.00
BaP	0.00	13.75	5.66	0.00	176.00	36.62
BkF	0.00	0.00	0.00	0.00	6.48	1.08
BbF	0.00	0.00	0.00	0.00	9.26	1.54
BghiP	0.00	0.00	0.00	0.00	0.09	0.02
IcdP	0.00	1.15	0.13	0.00	7.41	1.41
ΣPAH7	0.00	16.79	6.25	0.00	209.16	43.04
ΣPAH16	0.02	16.86	6.38	0.07	209.63	43.20

, none of the soil samples exceeded this benchmark, indicating a low potential for ecological risk under current contamination levels.

As presented in Table 7, the toxicity equivalent (TEQ) values of the 16 PAHs in the sediment samples from the YRD showed substantial variability, ranging from 0.07 to 209.63 ng/g, with a mean concentration of 43.2 ng/g. These results suggest that PAH contamination in sediments may pose a potential ecological threat. The seven carcinogenic PAHs were responsible for 99.64% of the total TEQ, with benzo[a]pyrene (BaP) contributing the largest portion at 84.78%, followed by benzo[a]anthracene (BaA) at 5.24%. At Site N5, the TEQ exceeded the ecological risk threshold by a factor of 6.35, which is likely linked to intensive anthropogenic activities in the surrounding area. Therefore, targeted pollution control strategies are necessary to mitigate the ecological risks associated with PAHs at this location.

3.5.2. Ecological Risk Results Based on ERL/ERM Thresholds

A comparison was conducted between the concentrations of 15 PAHs (excluding DahA, which was not detected in either soils or sediments) and the corresponding ERL and ERM benchmark values. As illustrated in Figure 7a, the majority of individual PAH concentrations were below their respective ERL thresholds, suggesting minimal ecological risk. Nevertheless, at certain sites, naphthalene (Nap) in soils and fluorene (Flu) in sediments exceeded the ERL values, implying the potential for occasional biological toxicity. Additionally, the presence of indeno[1,2,3-cd]pyrene (IcdP) may also contribute to toxic effects. These findings indicate that different PAHs require targeted prevention and management strategies. Special attention should be given to mitigating contamination by Nap, Flu, and IcdP, particularly by controlling anthropogenic emission sources. Overall, as shown in Figure 7b, the concentrations of low-molecular-weight PAHs (LMW), high-molecular-weight PAHs (HMW), and total ΣPAH₁₆ in both soil and sediment samples remained below their ERL reference values, indicating generally favorable environmental conditions with no significant ecological risk observed.

3.6. Health Risk Assessment of the Soil PAHs

Based on the incremental lifetime cancer risk (ILCR) model, the average ILCR values for both adults and children across the three exposure pathways—ingestion, inhalation, and dermal contact—in the surface soils of the YRD were all below 10⁻⁹, indicating an absence of significant carcinogenic risk (

Table 8. ILCR values of the PAHs in soils under the three exposure pathways.

Population	Statistical Value	ILCRingestion	ILCRinhalation	ILCRdermal	ILCRs
Adult	Maximum	1.93 × 10−11	1.49 × 10−15	3.42 × 10−11	5.35 × 10−11
	Minimum	2.85 × 10−14	2.21 × 10−18	5.07 × 10−14	7.92 × 10−14
	Mean	7.3 × 10−12	5.66 × 10−16	1.3 × 10−11	2.03 × 10−11
Children	Maximum	9.63 × 10−12	1.87 × 10−16	1.2 × 10−11	2.16 × 10−11
	Minimum	1.43 × 10−14	2.77 × 10−19	1.78 × 10−14	3.21 × 10−14
	Mean	3.65 × 10−12	7.07 × 10−17	4.55 × 10−12	8.2 × 10−12

). Among the exposure routes, dermal contact represented the primary pathway for adults, presenting higher cancer risk compared to that observed for children. This difference is likely due to adults’ larger skin exposure area and longer duration of environmental contact. Conversely, children showed a slightly elevated cancer risk through soil ingestion (3.65 × 10⁻¹²) relative to adults (7.3 × 10⁻¹²), a pattern that may result from common childhood behaviors such as hand-to-mouth activity. The ILCR values associated with inhalation exposure were approximately 5–6 orders of magnitude lower than those for ingestion and dermal contact, suggesting that volatilized PAHs in soil posed minimal risk and could be considered negligible. Overall, dermal absorption and ingestion were identified as the dominant routes of human exposure to soil-borne PAHs. Beyond the direct toxicological effects of the parent compounds, some high-molecular-weight PAHs—such as benzo[a]pyrene (BaP) and indeno[1,2,3-cd]pyrene (IcdP)—can undergo metabolic activation via cytochrome P450 enzymes in humans and other organisms. This biotransformation leads to the formation of reactive intermediates, including epoxides and diol epoxides, which are capable of forming DNA adducts, initiating mutations, and ultimately contributing to carcinogenesis. These mechanisms highlight the importance of ongoing surveillance and risk management in areas with elevated BaP-equivalent concentrations [57,58].

4. Conclusions

This study systematically evaluated the concentration levels, compositional characteristics, and potential ecological and human health risks of 16 priority PAHs in uncultivated land soils and coastal beach sediments of the YRD. The results revealed that while soil PAHs posed negligible ecological and carcinogenic risks, sediment contamination was more pronounced—particularly in northern coastal areas—where elevated concentrations of high-molecular-weight compounds were detected. Petroleum pollution and combustion-related sources were found to be the primary contributors. Given the spatial distribution of PAHs and their associated toxicities, targeted pollution control is recommended. Monitoring should be intensified in high-risk zones, especially for Nap, Flu, and IcdP, which showed elevated levels and toxic equivalency. In addition to enhanced surveillance, practical mitigation strategies such as vegetative buffer zones, sediment amendment using sorptive materials, or low-impact dredging should be considered in hotspot areas. Given the limited number of sediment samples (n = 6), the spatial interpretation of sediment PAH contamination should be treated cautiously, and future studies are encouraged to incorporate more extensive sampling to improve spatial resolution. These interventions would support long-term ecological restoration and contribute to evidence-based environmental governance in the YRD.