A Kinetic Study on the Accumulation of No.0 Fuel Oil and Pinghu Crude Oil Water-Accommodated Fraction in Exopalaemon carinicauda

Abstract

The kinetic parameters of No.0 fuel oil and Pinghu crude oil water-accommodated fractions (WAFs) during accumulation and elimination in Exopalaemon carinicauda were quantified using a semi-static two-compartment kinetic model. The accumulation phase data were analyzed via nonlinear regression to obtain kinetic parameters, yielding critical values including the uptake rate constant (k₁), elimination rate constant (k₂), bioconcentration factor (BCF), equilibrium body burden (C_Amax), and biological half-life (B_1/2). Modeling results demonstrated distinct kinetic parameters for the two oils. For No.0 fuel oil, the average values were k₁ = 5.21; k₂ = 0.1105; BCF = 48.98; C_Amax = 2.95 mg/kg; and B_1/2 = 6.40 days. For Pinghu crude oil, the averages were k₁ = 10.25; k₂ = 0.1044; BCF = 98.15; C_Amax = 8.48 mg/kg; and B_1/2 = 6.64 days. The uptake rate constant (k₁) and BCF generally decreased with increasing petroleum hydrocarbon exposure concentrations in ambient seawater, while the elimination rate constant (k₂) remained relatively constant across different concentrations. C_Amax increased proportionally with the petroleum hydrocarbon exposure concentration. Goodness-of-fit tests confirmed that the petroleum hydrocarbon concentrations in the experimental data were well described by the semi-static two-compartment model. Throughout the testing period, the concentration of No.0 fuel oil in Exopalaemon carinicauda remained lower than that of Pinghu crude oil.

1. Introduction

Petroleum hydrocarbons are of great concern due to their complex nature and environmental impacts. Human activities such as exploitation, refining, storage, transportation, and use are the main ways for petroleum hydrocarbons to enter the marine environment [1,2]. Among them, oil spill accidents in nearshore environments are particularly harmful, as they affect coastal ecosystems where species like Exopalaemon carinicauda are abundant in the photic zone [3]. When large-scale oil pollutants enter the ocean, a remarkable feature is the formation of a film of varying thickness on the sea surface. This film interferes with the normal exchange of gas, energy, and water at the sea–air interface and affects photosynthesis [4]. Moreover, the dissolved part can poison phytoplankton [5], zooplankton [6], fish eggs [7], and larvae [8] as well. In addition, petroleum hydrocarbons that enter the sediment through adsorption, flocculation, and precipitation can also cause short-term or long-term toxic hazards to various benthic organisms [9]. Even its pollution can cause mass deaths of pelagic organisms [10]. Consequently, oil pollution not only devastates the foundation of material circulation and energy flow within the marine ecosystem but also has the potential to ultimately disrupt the balance of the food chain, decrease the marine biodiversity index, lead to the decline of marine living resources, and weaken the marine ecosystem [9]. The degradation of petroleum pollutants in the marine environment is slow, and their impact is long-lasting. Although some hydrocarbons enter the atmosphere through evaporation, photochemical reactions, and microbial degradation, the majority persist as the WAF in seawater, and its toxicity in seawater is mainly from this part [11]. The extent of the direct damage inflicted by oil pollution on the ocean is often closely related to the persistence of the pollution, a characteristic that can sometimes impact marine life more than the toxicity itself [12].

The acquisition of enrichment kinetic parameters for petroleum hydrocarbon pollutants in marine organisms is essential for studying the long-term bioaccumulative effects of these pollutants, understanding the impact of petroleum hydrocarbon pollution on marine ecosystems, and establishing multimedia environmental models. It is also of great significance for studying the migration, transformation, and fate of petroleum hydrocarbons in the marine environment and for environmental assessment. Currently, research on the concentration of petroleum hydrocarbons in marine organisms both domestically and internationally primarily focuses on shellfish [13,14,15], while bioenrichment in shrimp merely indicates the accumulation and release of certain hydrocarbons within their bodies [16,17], which requires further investigation.

To address these research gaps, based on the semi-static two-compartment dynamic model [10], No. 0 fuel oil and Pinghu crude oil WAFs were selected as test materials, and Exopalaemon carinicauda was selected as the study organism. The kinetic parameters of No.0 fuel oil and Pinghu crude oil water-accommodated fraction (WAF) during accumulation and elimination in Exopalaemon carinicauda were quantified using a semi-static two-compartment kinetic model. Through dynamic monitoring of petroleum hydrocarbon concentrations during the accumulation and elimination phases, combined with nonlinear curve fitting of the data and model goodness-of-fit testing, we quantified the bioconcentration factor (BCF) of petroleum hydrocarbons in Exopalaemon carinicauda. This approach enabled systematic characterization of kinetic parameters and comparative analysis of bioaccumulation patterns between different petroleum WAFs. It also helped explore the accumulation kinetics of petroleum hydrocarbons in the body of Exopalaemon carinicauda, facilitating research, prediction, and understanding of marine organisms’ response to petroleum hydrocarbon pollution and providing basic data for the prediction of ecological risks.

2. Materials and Methods

2.1. Experimental Materials

2.1.1. Experimental Animals

The experimental Exopalaemon carinicauda were collected from a breeding pond in Qidong City, Jiangsu Province. Prior to the experiment, the shrimp were acclimated for 15 days in filtered seawater at 24 °C with daily feeding to adapt to laboratory conditions. Healthy individuals were selected and confirmed as mixed-sex adults via external morphological inspection, with an average weight of 2.71 ± 0.43 g and body length of 19.01 ± 0.50 cm. A total of 1680 individuals were used in the experiment (4 concentration groups × 3 replicates × 70 individuals per replicate × 2 oil types).

2.1.2. Experimental Reagents and Containers

The seawater used in the experiment was collected from a natural marine area with a salinity of 20–21 and a pH of 8.10–8.40 and subjected to sedimentation, sand filtration, and 24 h aeration prior to use. The test oils included commercial No.0 fuel oil and Donghai–Pinghu crude oil, and the experimental animals were housed in 90 L polyethylene tanks with a working volume of 40 L.

2.2. Preparation of Experimental Water-Accommodated Fraction (WAF)

Stock solutions of No.0 fuel oil and crude oil were prepared by mixing oil with filtered seawater at a 1:10 (V:V) ratio, followed by continuous stirring at 1000 rpm on a magnetic stirrer for 24 h. The mixture was then allowed to settle for 3 h, and the aqueous phase was separated by visual phase distinction (no visible oil droplets in the aqueous phase) before transfer to mother liquor storage bottles [18]. Petroleum hydrocarbon concentrations were quantified using a Shimadzu UV-1800 spectrophotometer (Shimadzu Corporation, Kyoto, Japan) at 254 nm [19].

2.3. Experimental Methods

The experiment was divided into accumulation and elimination phases, lasting 18 days and 15 days, respectively. The accumulation phase adopted semi-static conditions, where the entire volume of WAF was replaced daily to maintain stable exposure concentrations. In contrast, the elimination phase used a flow-through system, where clean seawater was continuously supplied to simulate natural environmental conditions and avoid artificial interference from frequent water changes, which could affect the elimination kinetics. Preliminary experiments were carried out to determine the most appropriate exposure concentrations for bioaccumulation assays. Specifically, 96 h acute toxicity tests were conducted with a wide range of concentrations (0.01–0.5 mg/L for No.0 fuel oil WAF and 0.005–0.3 mg/L for Pinghu crude oil WAF) to assess mortality rates. Concentrations were selected to ensure measurable accumulation while avoiding excessive mortality (>20%), as high mortality could disrupt the kinetic analysis. Based on the pre-test results, the final concentration gradients were set as follows: No.0 fuel oil WAF at 0.12 mg/L, 0.06 mg/L, 0.02 mg/L, and 0 mg/L (control); Pinghu crude oil WAF at 0.25 mg/L, 0.05 mg/L, 0.01 mg/L, and 0 mg/L (control). These concentrations are consistent with realistic exposure levels reported in coastal areas affected by oil spills, where WAF concentrations of petroleum hydrocarbons typically range from 0.01 to 0.3 mg/L. This ensures the ecological relevance of our experimental design. Each tank housed 70 Exopalaemon carinicauda individuals, with continuous aeration to maintain a dissolved oxygen level of more than 5.00 mg/L. The water temperature during the experiment was 23.6–25.4 °C.

Accumulation phase: The accumulation experiment was conducted using a semi-static method. Each tank contained 40 L of seawater, with complete replacement of the entire volume using freshly prepared WAF every 24 h. Any Exopalaemon carinicauda exhibiting abnormal behavior or death was removed promptly during each water change. The initial petroleum hydrocarbon content in the shrimp was measured before the experiment began. The shrimp were fed commercial feed from Qingdao Liuhe Feed Co., Ltd. (Qingdao, China) at a rate of 2% of their body weight, twice daily at 08:00 and 18:00 h. The PAH-contaminated waters were reprepared to maintain the set concentration gradients. For sample collection, 5 individuals of Exopalaemon carinicauda were taken from each tank on days 1, 4, 8, 16, and 19. These samples were shelled, homogenized, and quickly frozen for subsequent analysis. For the control group, 5 individuals were sampled at the same time points as the treatment groups (i.e., days 1, 4, 8, 16, and 19 during accumulation; days 20, 21, 23, 27, and 35 during elimination) to monitor baseline petroleum hydrocarbon levels throughout the experiment. This ensured that any changes in the treatment groups could be distinguished from natural fluctuations in background concentrations.

Elimination phase: Following the accumulation phase, the experimental solutions in each tank were completely drained, and the depuration of accumulated petroleum hydrocarbons from Exopalaemon carinicauda was examined under flow-through conditions. The shrimp were fed as previously described. Samples were collected on days 20, 21, 23, 27, and 35, processed identically to those in the accumulation phase, and flash-frozen for analysis.

Accumulation stage: This stage focuses on the process from external exposure to bioaccumulation. Semi-static conditions ensure data reliability through stable concentrations.

Elimination stage: This stage focuses on the release process from organisms to the environment. The flow-through system helps maintain stable water quality and animal health, avoiding artificial interference such as frequent water changes that could affect elimination kinetics.

Independence of parameter calculation: Kinetic parameters are fitted based on independent data from the two stages, with no mutual influence. Accumulation data under semi-static conditions are calculated via nonlinear regression using Equation (3), while elimination data under the flow-through system are fitted using Equation (4). The models have different assumptions but are both statistically validated.

2.4. Sample Analysis

The content of petroleum hydrocarbons in Exopalaemon carinicauda was determined using a fluorescence spectrophotometer (Shimadzu RF-5301PC, Shimadzu Corporation, Kyoto, Japan) [20].

Tissue samples of Exopalaemon carinicauda (shell and non-edible parts removed) were homogenized, and petroleum hydrocarbons were extracted using n-hexane/dichloromethane. After centrifugation, the organic phase was collected, and the extraction was repeated to combine extracts. Interfering substances were removed via silica gel/alumina column purification. Extracts were concentrated under nitrogen and reconstituted in n-hexane. The Shimadzu RF-5301PC fluorometer (Shimadzu Corporation, Kyoto, Japan) was calibrated with petroleum hydrocarbon standard solutions. Measurements were performed at excitation (Ex = 310 nm) and emission (Em = 360 nm) wavelengths, with 2–3 replicates per sample. The limit of detection (LOD) was 0.01 mg/kg, and the limit of quantification (LOQ) was 0.03 mg/kg. Recovery rates for spiked samples ranged from 85% to 92%, ensuring data reliability.

2.5. Semi-Static Two-Compartment Kinetic Model

The semi-static two-compartment kinetic model typically assumes that the bioaccumulation of pollutants in organisms can be approximated as a two-phase partitioning process between the aqueous and organic phases [10]. It considers both the accumulation and release processes, i.e., the absorption, accumulation, and release of pollutants by organisms from the environment. The accumulation and release processes can be described by first-order kinetics. The model is described below (Figure 1).

Aqueous phase:

$${\displaystyle \frac{\mathrm{d}{\mathrm{C}}_{\mathrm{W}}}{{\mathrm{d}}_{\mathrm{t}}}}=0$$

(1)

Organic phase:

$${\displaystyle \frac{\mathrm{d}{\mathrm{C}}_{\mathrm{A}}}{{\mathrm{d}}_{\mathrm{t}}}}={\mathrm{k}}_1{\mathrm{C}}_{\mathrm{W}}-\left({\mathrm{k}}_2+{\mathrm{k}}_{\mathrm{m}}\right){\mathrm{C}}_{\mathrm{A}}$$

(2)

where k₁ is the bioaccumulation rate constant; k₂ is the release rate constant; k_v is the volatilization rate constant; k_m is the metabolic rate constant of the organism; C_W is the concentration of pollutants in the water (mg/L); and C_A is the concentration of pollutants in the organism (mg/kg). During the derivation of the equations, the natural volatilization of pollutants in the water (k_v) and the metabolic rate of the organism (k_m) are neglected.

The accumulation process (0 < t < t*) follows the first-order kinetic equation:

$${\mathrm{C}}_{\mathrm{A}}={\mathrm{C}}_0+{\displaystyle \frac{{\mathrm{C}}_{\mathrm{W}}{\mathrm{k}}_1}{{\mathrm{k}}_2\left(1-{\mathrm{e}}^{-{\mathrm{k}}_2\mathrm{t}}\right)}}$$

(3)

The elimination process (t > t*) is described by

$${\mathrm{C}}_{\mathrm{A}}={\displaystyle \frac{{\mathrm{C}}_{\mathrm{W}}{\mathrm{k}}_1}{{\mathrm{k}}_2\left({\mathrm{e}}^{-{\mathrm{k}}_2\left(\mathrm{t}-{\mathrm{t}}^{\mathrm{*}}\right)}-{\mathrm{e}}^{-{\mathrm{k}}_2\mathrm{t}}\right)}}$$

(4)

From Equations (3) and (4), k₁ and k₂ can be obtained through nonlinear fitting. Theoretically, at equilibrium, the bioconcentration factor (BCF) is given by

$$\mathrm{B}\mathrm{C}\mathrm{F}={\displaystyle \frac{{\mathrm{k}}_1}{{\mathrm{k}}_2}}={\displaystyle \frac{\mathrm{l}\mathrm{i}\mathrm{m}{\mathrm{C}}_{\mathrm{A}}}{{\mathrm{C}}_{\mathrm{W}}\left(\mathrm{t}\to \mathrm{\infty }\right)}}$$

(5)

The biological half-life, which is the time required for the organism to release half of the accumulated pollutants through its life activities, is expressed as follows:

$${\mathrm{B}}_{{\displaystyle \frac{1}{2}}}={\displaystyle \frac{\mathrm{l}\mathrm{n}2}{{\mathrm{k}}_2}}$$

(6)

The maximum accumulation of pollutants in the organism at equilibrium is given by

$${\mathrm{C}}_{\mathrm{A}\mathrm{m}\mathrm{a}\mathrm{x}}=\mathrm{B}\mathrm{C}\mathrm{F}\times {\mathrm{C}}_{\mathrm{W}}$$

(7)

Even if equilibrium is not reached, the semi-static two-compartment kinetic model can still be used to calculate the kinetic parameters under theoretical equilibrium conditions.

2.6. Data Processing and Goodness-of-Fit

Nonlinear curve fitting analysis of petroleum hydrocarbon content in Exopalaemon carinicauda during accumulation and depuration phases was conducted using OriginPro 8 software from OriginLab Corporation (Northampton, MA, USA). The goodness-of-fit of the semi-static two-compartment kinetic model was evaluated through determination of the coefficient of determination R². Model significance was assessed via an F-test, while agreement between predicted and observed values was analyzed using a paired t-test with α = 0.05. Statistical analysis was based on triplicate tanks (n = 3), with data being expressed as mean ± standard error.

3. Results

3.1. Results and Analysis

The dynamic monitoring of petroleum hydrocarbons in Exopalaemon carinicauda during the accumulation and release processes was conducted, and the results were subjected to nonlinear fitting using Equations (3) and (4) to obtain accumulation and release curves for different exposure concentrations (Figure 2). During the accumulation phase, the most significant initial increase in the petroleum hydrocarbons was observed in Exopalaemon carinicauda, exhibiting a pattern of rapidly absorbing petroleum hydrocarbons. For No.0 fuel oil WAF, the greatest increase within the first 3 days was noted in the 0.12 mg/L group, with a 15.29-fold increase compared to the baseline. For crude oil WAF, the greatest increase was observed in the 0.25 mg/L group, with a 52.95-fold increase. In the middle and late stages, the absorption rate of petroleum hydrocarbons by Exopalaemon carinicauda gradually slowed. Over the last 3 days, the increase in the 0.12 mg/L No.0 fuel oil WAF group was only 0.12-fold, and in the 0.25 mg/L crude oil WAF group, it was only 0.10-fold, with both tending toward equilibrium. By the end of the accumulation phase, the highest hydrocarbon concentrations of petroleum in Exopalaemon carinicauda were 32.95 mg/kg (0.25 mg/L group) for crude oil WAF and 8.09 mg/kg (0.12 mg/L group) for No.0 fuel oil WAF, respectively.

During the release phase, the petroleum hydrocarbon content in Exopalaemon carinicauda decreased sharply in the early stage, exhibiting a linear decreasing trend. For No.0 fuel oil WAF, the greatest decrease on the first day of release occurred in the 0.12 mg/L group, with a 26.21% reduction. For crude oil WAF, the greatest decrease was in the 0.25 mg/L group, with a 24.09% reduction. As the release period extended, the rate of petroleum hydrocarbon elimination from Exopalaemon carinicauda slowed. In the final period (days 27–35), despite an 8-day duration, the reduction in the 0.12 mg/L No.0 fuel oil WAF group was only 20.07%, and in the 0.25 mg/L crude oil WAF group, it was only 12.23%. After 15 days of release, the petroleum hydrocarbon content in Exopalaemon carinicauda remained significantly higher than the baseline (control group). Residual hydrocarbons were 21.46% and 91.17% of the peak accumulation levels for No.0 fuel oil and crude oil WAF, respectively. In the highest concentration groups, residual levels were 21.46- and 91.17-fold higher than the baseline for No.0 fuel oil and crude oil WAF, respectively.

3.2. Enrichment Kinetic Parameters of No.0 Fuel Oil and Crude Oil WAF at Different Concentrations in Exopalaemon Carinicauda

Through the nonlinear curve fitting of the accumulation and release processes of No.0 fuel oil and crude oil WAF in Exopalaemon carinicauda, the absorption rate constant k₁ and the release rate constant k₂ were obtained. Then, according to Formulas (5)–(7), other kinetic parameters such as BCF, C_Amax, and B_1/2 were obtained (

Table 1. Kinetic parameters of accumulation of No.0 fuel oil and Pinghu crude oil in E. carinicauda at different concentrations.

Oils	Concentration (mg/L)	k1	k2	BCF	CAmax(mg/kg)	B1/2(d)
No.0 Fuel Oil WAF	0.12	4.16 ± 0.32 a	0.1333 ± 0.010 b	31.21 ± 2.15 a	3.75 ± 0.28 a	5.20 ± 0.31 a
No.0 Fuel Oil WAF	0.06	5.35 ± 0.41 b	0.0985 ± 0.008 a	54.29 ± 3.62 b	3.26 ± 0.21 a	7.03 ± 0.45 b
No.0 Fuel Oil WAF	0.03	6.12 ± 0.38 b	0.0997 ± 0.007 a	61.42 ± 4.05 b	1.84 ± 0.15 a	6.95 ± 0.38 b
Crude Oil WAF	0.25	8.14 ± 0.52 c	0.1025 ± 0.009 a	79.37 ± 5.21 c	19.84 ± 1.32 c	6.76 ± 0.29 a
Crude Oil WAF	0.05	9.16 ± 0.63 d	0.1059 ± 0.006 a	86.47 ± 4.89 d	4.32 ± 0.33 a	6.54 ± 0.32 a
Crude Oil WAF	0.01	13.47 ± 0.75 e	0.1047 ± 0.008 a	128.61 ± 6.93 e	1.29 ± 0.11 a	6.62 ± 0.27 a

Symbol Legend: Superscripts (^a/^b/^c/^d/^e) indicate significant differences, determined by one-way ANOVA followed by Tukey’s post hoc test (^a/^b/^c: p < 0.05; ^d/^e: p < 0.01). Trend with Increasing Exposure Concentration: k₁: Decreased significantly (e.g., from 13.47 d⁻¹ at 0.01 mg/L to 8.14 d⁻¹ at 0.25 mg/L in crude oil WAF). k₂: No significant change (range: 0.0985–0.1333 d⁻¹ across all groups). BCF: Decreased significantly (e.g., from 128.61 at 0.01 mg/L to 79.37 at 0.25 mg/L in crude oil WAF). C_Amax: Increased proportionally (e.g., from 1.29 mg/kg at 0.01 mg/L to 32.95 mg/kg at 0.25 mg/L in fuel oil WAF). B_1/2: Slightly longer for crude oil (6.64 days) vs. fuel oil (6.40 days), but no significant difference.

). The average values of the absorption rate constant k₁ of No.0 fuel oil and crude oil WAF in Exopalaemon carinicauda are 5.21 and 10.25, respectively, and both decrease with increasing ambient petroleum hydrocarbon concentrations in the ambient water body. The average values of the release rate constant k₂ of No.0 fuel oil and crude oil WAF are 0.1105 and 0.1044, respectively, and there is no obvious statistical correlation between these values and the concentration of petroleum hydrocarbons in the ambient water body. The average values of the bioconcentration factor BCF of No.0 fuel oil and crude oil WAF are 48.98 and 98.15, respectively, and both decrease with the increase in the concentration of petroleum hydrocarbons in the external water body. The average values of C_Amax in organisms in the equilibrium state are 2.95 and 8.48 mg/kg, respectively. Both values increase with the rise in petroleum hydrocarbon concentration in the external water body, indicating a generally positive statistical correlation. The biological half-life B_1/2 of crude oil in Exopalaemon carinicauda is slightly higher than that of No.0 fuel oil WAF. The average value of No.0 fuel oil WAF is 6.40 d, and the average value of crude oil WAF is 6.64 d.

3.3. Goodness-of-Fit Test of the Model

When conducting a nonlinear curve fitting for petroleum hydrocarbons in the body of Exopalaemon carinicauda during the accumulation and release process, the fitting results are validated using the coefficient of determination (R²). The range of R² values for the fitting curves of each group is 0.8331–0.9978 (

Table 2. Summary of statistical information to assess the goodness-of-fit of the two compartment models applied in the accumulation of No.0 fuel oil and Pinghu crude oil in E. carinicauda.

Oils	Concentration (mg/L)	R2	F-Test p-Value	t-Test p-Value
No.0 Fuel Oil WAF	0.12	0.9978	0.0275	0.3957
No.0 Fuel Oil WAF	0.06	0.9883	0.0391	0.4015
No.0 Fuel Oil WAF	0.03	0.9783	0.0297	0.4186
Crude Oil WAF	0.25	0.9892	0.0324	0.3944
Crude Oil WAF	0.05	0.9862	0.0366	0.3929
Crude Oil WAF	0.01	0.8331	0.0113	0.4222

), indicating a good degree of fit. Additionally, the F-test results (Table 2) indicate that the model regression equation is significant (p < 0.05). Furthermore, based on the model validity, a paired t-test was used to compare the model output values with the actual values. Under the condition of α = 0.05, all p-values were greater than α (Table 2), indicating that the difference between the model output results and the actual values is not significant. These test results demonstrate that under the conditions of this experiment, the semi-static two-compartment kinetic model is applicable to the bioaccumulation kinetics study of Exopalaemon carinicauda exposed to No.0 fuel oil and crude oil WAF.

4. Discussion

This study explored the bioaccumulation and depuration dynamics of petroleum hydrocarbons in Exopalaemon carinicauda using a semi-static two-compartment model, with a focus on the regulatory patterns of key kinetic parameters and their ecological implications. The results indicate that Exopalaemon carinicauda exhibit distinct accumulation and elimination strategies compared to non-acclimated individuals, reflecting adaptive responses to petroleum hydrocarbon exposure—consistent with findings in other aquatic organisms, where prior exposure enhances stress resilience [19,21].

Exopalaemon carinicauda showed rapid initial accumulation of petroleum hydrocarbons, with a 15.29–52.95-fold increase within 3 days. This aligns with observations in Penaeus vannamei and Mytilus edulis, where passive diffusion and lipid partitioning drive early uptake of hydrophobic compounds [16,22]. Notably, crude oil WAF induced higher accumulation than No.0 fuel oil WAF. This is likely due to its higher content of high-molecular-weight PAHs, which have stronger hydrophobicity (log Koc > 5) and greater affinity for lipid-rich tissues, as reported in PAH bioaccumulation studies [23]. This mirrors reports in bivalves, where PAH hydrophobicity correlates with bioaccumulation capacity [24].

The concentration-dependent reduction in uptake rate (k₁) and bioconcentration factor (BCF) suggests a potential inhibitory effect at high exposures, similar to findings in Litopenaeus setiferus, where elevated PAH levels impair the gill function and reduce uptake efficiency [23]. In contrast, the independence of the elimination rate (k₂) from the concentration indicates that depuration is primarily a passive process, consistent with observations in Hemigrapsus nudus, where naphthalene clearance relies on diffusion rather than metabolic activity [21]. This passivity may explain the persistent residues in Exopalaemon carinicauda (21.46–91.17-fold above baseline after 15 days), exceeding the depuration capacity of species like Ruditapes philippinarum [15].

Ecologically, Exopalaemon carinicauda, as a key prey species, may potentially facilitate trophic transfer of petroleum hydrocarbons. This is consistent with observations from the Prestige oil spill, where PAH accumulation in invertebrates was associated with reproductive declines in their predators, although direct evidence for such transfer in the present study is limited [24]. The higher residual levels of crude oil WAF further amplify risks, given the greater toxicity and recalcitrance of its components [25]. Long-term impacts may include altered metabolic processes, such as changes in enzyme activity, as observed in other marine organisms following PAH exposure [21,26]. These findings highlight the need for species-specific risk assessments, as current standards based on bivalves may underestimate crustacean-related risks [22].

These findings inform coastal management and policy: The rapid initial accumulation (52.95-fold in 3 days for crude oil WAF) demands targeted oil spill response strategies for Exopalaemon carinicauda habitats, prioritizing this key prey species to curb trophic pollutant spread [27]. Regulatory standards must include crustacean-specific thresholds, as bivalve-based metrics underestimate risks from species like Exopalaemon carinicauda with higher lipid-driven accumulation [19,22]. Restoring seagrass beds (reducing hydrocarbon bioavailability by 40–60% [28]) and mangroves in nursery grounds can lower exposure, mirroring 30–50% reduced PAH transfer in restored tropical estuaries. Optimizing aquaculture—adjusting densities in oil-prone areas and selecting for enhanced depuration, as with heat-tolerant fish—would also boost spill resilience.

Methodologically, the strong model fit (R²=0.8331–0.9978) validates the two-compartment model’s applicability to Exopalaemon carinicauda, which is comparable to its use in quantifying hydrocarbon kinetics in Mytilus edulis [22]. However, the model’s simplification of metabolic processes may limit its accuracy under field conditions, where variables like temperature and salinity can alter kinetics [11,21]. Future research should incorporate environmental variables and metabolic rate constants (k_m) to improve model realism.

Our findings on the accumulation and depuration kinetics of petroleum hydrocarbons in Exopalaemon carinicauda directly inform operational oil spill response strategies. For instance, the rapid initial accumulation (up to 52.95-fold in 3 days for crude oil WAF) highlights the need for timely containment of spills in nearshore habitats where this species is abundant. Additionally, the effectiveness of oil spill response measures can influence the pollutant bioavailability and subsequent depuration in marine organisms, emphasizing the importance of integrating species-specific kinetic data into response planning [29].

5. Conclusions

This study investigated the petroleum hydrocarbon accumulation and depuration dynamics in Exopalaemon carinicauda using a semi-static two-compartment model, revealing distinct patterns: rapid initial uptake with a 15.29–52.95-fold increase within 3 days followed by slowed accumulation, and depuration exhibiting a similar decelerating trend. The maximum accumulation reached 32.95 mg/kg for crude oil WAF at 0.25 mg/L and 8.09 mg/kg for No.0 fuel oil WAF at 0.12 mg/L, with both significantly exceeding baseline levels. Kinetic parameters derived from the model exhibited concentration-dependent trends. The uptake rate (k₁) and BCF decreased with increasing exposure, while the elimination rate (k₂) was concentration-independent. The equilibrium accumulation (C_Amax) increased with exposure, indicating a positive correlation. Crude oil WAF induced higher bioaccumulation, with a BCF of 98.15, but slower depuration compared to No.0 fuel oil WAF, with a BCF of 48.98, which is likely attributable to its high-molecular-weight PAHs with stronger hydrophobicity. The model fit was robust, with an R² of 0.8331–0.9978 and p < 0.05, validating its utility for quantifying petroleum hydrocarbon kinetics in Exopalaemon carinicauda. These findings highlight the ecological risks of petroleum hydrocarbon exposure in Exopalaemon carinicauda that are posed by persistent residues and trophic transfer potential and emphasize the need for targeted monitoring and species-specific regulatory frameworks in oil spill-prone coastal zones.