疏水性有机污染物进入水体后，由于其具有较高的辛醇-水分配系数和难溶于水的特征，易与悬浮颗粒物相结合，然而目前有关悬浮颗粒结合态疏水性有机物的生物有效性不清楚，尤其是有关悬浮颗粒物对疏水性有机污染物在鱼体内生物富集的影响不清楚，严重影响了疏水性有机污染物的生态和健康风险评价。我们已有研究表明鱼类摄食含有污染物的食物能够影响疏水性有机污染物的生物富集，摄食悬浮颗粒物与摄食食物相似，因此，我们推测摄食含有污染物的泥沙颗粒也能影响污染物在鱼体内的生物富集，且这种影响与悬浮颗粒物的浓度，粒径和组成等相关，另外，由于疏水性有机污染物在生物体不同组织的富集过程存在差异，所以推测悬浮颗粒物对生物体不同组织的生物富集的影响可能不同。因此，为验证这些科学假设，本文选取典型疏水性有机污染物多环芳烃为研究对象，采用被动给样装置控制水相多环芳烃的自由溶解态浓度，研究悬浮颗粒物浓度和粒径对多环芳烃在模式脊椎动物（斑马鱼）体内富集动力学和富集稳态的影响，分析悬浮颗粒物对多环芳烃在斑马鱼不同组织内生物富集的影响；综合分析悬浮颗粒物对多环芳烃的吸附作用、悬浮颗粒被斑马鱼的摄食作用以及肠道内颗粒结合态多环芳烃的解吸作用等多过程，进而探讨悬浮颗粒物影响的因素，揭示悬浮颗粒结合态多环芳烃对斑马鱼的生物有效性及影响机制，本论文的主要研究结果如下：

所构建的被动给样装置(PDMS平板)能够使水相多环芳烃的自由溶解态浓度维持不变。悬浮颗粒物能够通过摄食方式进入斑马鱼体内，且不同粒径(63-106 μm，20-63 μm和<20 μm)悬浮颗粒物在斑马鱼消化道内的摄食量无显著性差异(p > 0.05)，悬浮颗粒物的摄食对斑马鱼体内的脂肪含量以及含水率没有显著的影响(p > 0.05)。

较低浓度的悬浮颗粒物（0.1 g·L^-1和0.5 g·L^-1）对荧蒽和芘在斑马鱼体内生物富集的影响结果表明，不管体系有无悬浮颗粒物，斑马鱼体内多环芳烃的含量均随暴露时间的增加而增加，暴露12 d后多环芳烃在斑马鱼体内基本达到富集稳态。当体系荧蒽和芘的自由溶解态浓度维持不变时，悬浮颗粒物浓度对多环芳烃在斑马鱼体内的富集稳态无显著影响，多环芳烃在斑马鱼体内的富集稳态浓度受多环芳烃在水相的自由溶解态浓度控制。但悬浮颗粒物的存在能够提高多环芳烃在斑马鱼体内的吸收和排出速率，如在前8 d的富集过程中，荧蒽和芘在0.5 g·L^-1悬浮颗粒物暴露体系的斑马鱼体内的吸收速率是不含悬浮颗粒物体系的两倍左右，前8-d的暴露过程中，荧蒽和芘在斑马鱼体内的富集量分别增加了16.4% - 109.3%和21.8% - 490.4%。

不同粒径悬浮颗粒物（63-106 μm，20-63 μm和<20 μm）对多环芳烃（菲- d10，蒽-d10，荧蒽-d10和芘-d10）在斑马鱼体内生物富集影响的结果表明，三种粒径的悬浮颗粒物（1 g·L^-1）都能提高氘代多环芳烃在斑马鱼体内(不管脂肪校正与否)的富集量，并且富集量随粒径的减小而增大，如富集20 h后，与暴露于无悬浮颗粒物体系的斑马鱼体内脂肪校正后的氘代多环芳烃含量相比，暴露于63-106 μm，20-63 μm和<20 μm悬浮颗粒物体系的斑马鱼体内脂肪校正后的氘代多环芳烃含量分别增加了12% - 72%，34% - 130%和60% - 196%。

多环芳烃在斑马鱼不同组织内的生物富集存在差异。整体来看，四种多环芳烃（菲，蒽，荧蒽和芘）在鱼皮中浓度最高，鱼肉中浓度最低。如在暴露16 d时，多环芳烃菲在斑马鱼不同组织内的富集浓度大小顺序为：鱼皮（4949 ± 186 ng/g） > 消化道（4164 ± 52 ng/g） ≈ 肝（4232 ± 112 ng/g） ≈ 性腺（4064 ± 218 ng/g） > 剩余其它组织（3655 ± 128 ng/g） > 鱼鳃（3003 ± 131 ng/g） > 鱼肉（1004 ± 34 ng/g）；多环芳烃在斑马鱼不同组织内的生物富集因子大小顺序为：鱼皮 > 消化道 ≈ 肝 ≈ 性腺 ≈ 剩余其它组织 > 鱼鳃 > 鱼肉。多环芳烃在不同组织内的富集量随组织内脂肪含量的增加而增大，但二者之间没有显著的相关性（p > 0.05)，说明组织的脂肪含量不是影响多环芳烃在鱼体不同组织间分布的决定性因素。进一步分析发现，多环芳烃在斑马鱼不同组织间的吸收和排出速率存在差异，如菲在不同组织内吸收速率大小顺序为肝 ≈ 消化道 > 鱼鳃 > 鱼皮 > 性腺 > 剩余其它组织 > 鱼肉，由此说明多环芳烃在不同组织内的吸收和排出速率也是影响其在不同组织富集量的重要因素。本研究的结果还表明，鱼皮与肝和肠器官组织一样是多环芳烃在斑马鱼体内的主要富集场所，且鱼皮可能是多环芳烃进入斑马鱼体内的不可忽视的途径之一。

不同粒径的悬浮颗粒物对多环芳烃在斑马鱼不同组织内生物富集影响的结果表明，不同粒径悬浮颗粒物对多环芳烃在斑马鱼不同组织内的富集稳态无显著影响，但在富集达到稳态前，暴露体系悬浮颗粒物（0.5 g·L^-1）的存在提高了多环芳烃在不同组织中的富集浓度。如在前8-d的暴露过程中，悬浮颗粒物的存在使得斑马鱼鱼肉中菲，蒽，荧蒽和芘的含量分别增加了9.9% - 38.0%，12.2% - 80.2%，10.7% - 42.3%，7.9% - 56.2%。且悬浮颗粒物对多环芳烃在斑马鱼不同组织中富集量的影响与悬浮颗粒物粒径呈负相关性，如暴露4 d时，菲在暴露于63-106 μm，20-63 μm和<20 μm悬浮颗粒物体系的斑马鱼鱼肉中的含量比在无悬浮颗粒物体系中的含量分别增加了11.4%，27.6%和31.7%。不同粒径的悬浮颗粒物改变了多环芳烃在斑马鱼不同组织中的富集速率，如与没有悬浮颗粒物的体系相比，菲，蒽，荧蒽和芘在有悬浮颗粒物体系的斑马鱼鱼肉中的吸收速率分别增加了22.8% - 67.1%，40.0% - 91.0%，28.0% - 52.8%和19.9% - 45.4%，而且增加量与悬浮颗粒物的粒径呈负相关关系，如荧蒽在含有63-106 μm，20-63 μm和<20 μm三种粒径的悬浮颗粒物体系的斑马鱼鱼肉中的吸收速率分别增加了28.0%，47.7%和52.8%。

上述结果表明，当体系多环芳烃的自由溶解态浓度维持不变时，悬浮颗粒物的存在能够对多环芳烃在斑马鱼体内的富集动力学产生影响，这是由于悬浮颗粒结合态多环芳烃部分具有生物有效性，其能够通过摄食作用进入斑马鱼消化道中，在肠道消化液的作用下，颗粒结合态多环芳烃发生再解吸而被斑马鱼吸收富集。颗粒结合态多环芳烃的浓度与颗粒物的组成和粒径有关，且其在颗粒物上的解吸也与颗粒物的粒径和组成相关。本研究中发现小粒径悬浮颗粒物对多环芳烃在斑马鱼体内生物富集动力学的影响更大，这可能是由于本研究中选取的小粒径颗粒物具有更小的黑碳与总有机碳比值，更高的溶解性有机碳，以及更小的粒径尺寸，这些因素都将使得小粒径颗粒物表面吸附的多环芳烃更容易解吸，进而增加了颗粒态多环芳烃的生物有效性。另外，悬浮颗粒物的存在增大了多环芳烃在鱼鳃中的富集量和吸收速率，表明鱼鳃在呼吸过程中与悬浮颗粒物不断接触，而且小粒径的悬浮颗粒接触更充分，可能导致与悬浮颗粒物弱结合的多环芳烃发生再解吸，被鱼鳃吸收进入斑马鱼体内，这可能也是悬浮颗粒影响多环芳烃在斑马鱼体内生物富集的另一机制。

本论文的研究结果表明，颗粒结合态多环芳烃部分具有生物有效性，颗粒摄食是多环芳烃在斑马鱼体内生物富集的主要途径之一。悬浮颗粒物对多环芳烃在斑马鱼体内生物富集的影响，不仅与悬浮颗粒物的浓度有关，还与悬浮颗粒的粒径和组成等因素有关。因此，在对河流水体尤其高泥沙含量的河流水体进行生态风险评估时，应考虑与悬浮颗粒物结合的疏水性有机污染物的生物有效性，而且要综合考虑泥沙含量、粒径和组成的影响。

Hydrophobic organic compounds (HOCs) are preferentially associated with suspended particles (SPS) in surface aquatic systems due to their high n-octanol-water partition coefficients and high hydrophobic characters; however, the bioavailability of HOCs associated with particles especially for fish is not fully understood, and this will cause inaccurate ecological risk assessment. Our previous study found that ingestion of food containing HOCs would affect the HOC bioaccumulation by zebrafish, because suspended particle ingestion is similar with food ingestion, we inferred that ingestion of particle-associated HOCs would also affect the HOC bioaccumulation by zebrafish, and the bioavailability of particle-associated HOCs was related with the particle size and composition. In addition, there is difference in the bioaccumlation of HOCs among different organism tissues, therefore, we also inferred that SPS would affect the bioaccumulation of HOCs in different tissues of organisms. In order to prove the above hypothesis, a passive dosing device (PDMS device) was used to control the freely dissolved concentrations (C_free) of polycyclic aromatic hydrocarbons (PAHs), and the influence of particle  concentration and particle size on PAH bioaccumulation by zebrafish (or different tissues of zebrafish) was investigated. In order to study the bioavailabity of PAHs associated with suspended particles, we discussed the the behavior of PAH adsorption by suspended particles, suspended particle ingestion by zebrafish, as well as the desorption of PAHs from particles ingested in the digestive tract of zebrafish. The results of the study were stated as follows:

 The freely dissolved concentrations of PAHs could be kept constant by the PDMS device; the particles can be ingested by zebrafish, and there was no significant difference (p > 0.05) in the SPS amount ingested by the zebrafish among the three different grain size SPS (63-106 μm, 20-63 μm, and <20 μm). In addition, the lipid contents and water contents in zebrafish were not affected obviously by the SPS ingestion (p > 0.05).

When the C_free of fluoranthene and pyrene was kept constant, the body burden of PAHs in zebrafish (excluding head and digestive tracts) increased with exposure time, and obtained steady state in the zebrafish tissues after 12-d exposure. The presence of different concentrations of SPS (0.1 g·L^-1 and 0.5 g·L^-1) did not significantly affect the steady state of PAH bioaccumulation in zebrafish, suggesting that the bioaccumulation steady state was controlled by the freely dissolved concentrations of PAHs in water. However, suspended particles promoted the uptake and elimination rate constants of PAHs to zebrafish. The uptake rate constants with 0.5 g/L suspended particle were approximately twice than those without suspended particles, and the body burden in zebrafish increased by 16.4% - 109.3% for pyrene and 21.8% - 490.4% for fluoranthene during the first 8-d exposure.

The concentrations (lipid-normalized or not) of PAHs (phenanthrene-d10, anthracene-d10, fluoranthene-d10 and pyrene-d10) in zebrafish were promoted in the presence of the three different sizes (63-106 μm, 20-63 μm, and <20 μm) of SPS (1 g·L^-1), and the PAH-d10 concentrations in zebrafish increased with the decreasing of the particle size. Compared with the systems without SPS, the lipid-normalized concentrations of PAHs-d10 increased by 12% - 72%, 34% - 130%, and 60% - 196%, respectively in zebrafish in systems with 63-106 μm, 20-63 μm, and <20 μm of SPS after exposure for 20 h.

There was difference in the bioaccumulation of PAHs in different tissues (skin, fish muscle, gill, digestive tract, liver, gonad, residual) of the zebrafish. Generally, the concentrations of PAHs were highest in the skin tissues, and lowest in the fish muscle tissues. For example, after 16-d exposure, the order of phenanthrene concentrations in different tissues of zebrafish was skin (4949 ± 186 ng·g^-1) > digestive tract (4164 ± 52 ng·g^-1) ≈ liver (4232 ± 112 ng·g^-1) ≈ gonad (4064 ± 218 ng·g^-1) > residual (3655 ± 128 ng·g^-1) > gill (3003 ± 131 ng·g^-1) > fish muscle (1004 ± 34 ng·g^-1); and the order of PAH bioaccumulation factors in different tissues was skin > digestive tract ≈ liver ≈ gonad ≈ residual > gill > fish muscle. PAH concentrations increased with the lipid contents in different tissues of the zebrafish, however, the correlation between PAH concentrations and lipid contents was not obvious (p > 0.05), and this indicated that lipid contents was not the only factor that determined the distribution of PAHs in different tissues of the zebrafish. Further, we found that the uptake and elimination rate constants of PAHs were different in different zebrafish tissues, for example, the order of the uptake rate constant of phenanthrene was liver ≈ digestive tract > gill > skin > gonad > residual > fish muscle, and this suggested that the uptake and elimination rates would also affected the distribution of PAHs in different tissues of the zebrafish. The distribution of PAHs indicted that skin, liver and digestive tract are the key bioaccumuation tissues of the zebrafih, and the route of uptake through skin was not neglectable for PAH accumulation in zebrafish.  

The bioaccumulation steady state of PAHs in different tissues of the zebrafish was not affected by the three different size suspended particles, however, the body burden of PAHs in different tissues of zebrafish increased in the presence of the three different size SPS (0.5 g·L^-1) before the steady state. For example, during the first 8-d exposure, compared with PAH concentration in muscles of the zebrafish cultured in the exposure system without suspended particles, phenanthrene, anthracene, fluoranthene and pyrene concentrations in muscles of zebrafish cultured in the exposure system with different size suspended particles increased by 9.9% - 38.0%, 12.2% - 80.2%, 10.7% - 42.3%, 7.9% - 56.2%, respectively. Generally, there was a negative correlation between the effect of SPS on PAH bioaccumulation contents in different tissues of the zebrafish and the particle size before the steady state of PAH bioaccumulation. For example, compared with the concentrations of phenanthrene in muscles of the zebrafish cultured in the exposure system without suspended particles, the concentrations of phenanthrene increased by 11.4%, 27.6% and 31.7%, respectively in the muscles of zebrafish cultured in the exposure system with 63-106 μm, 20-63 μm, and <20 μm suspended particles. The uptake rates of PAH in different tissues of zebrafish were promoted by the three different size suspended particles, for example, compared with the uptake rates of PAH in muscles of the zebrafish cultured in the exposure system without suspended particles, the uptake rates of phenanthrene, anthracene, fluoranthene and pyrene in muscles of zebrafish cultured in the exposure systems with different size suspended particles increased by 22.8% - 67.1%, 40.0% - 91.0%, 28.0% - 52.8%, and 19.9% - 45.4%, respectively; and the effect on uptake rates was related with the size of the particles, for example, compared with the uptake rates of fluoranthene in the muscles of the zebrafish cultured in the exposure system without suspended particles, the uptake rates increased by 28.0%, 47.7% and 52.8%, respectively in the muscles of zebrafish cultured in the exposure system with 63-106 μm, 20-63 μm, and <20 μm suspended particles.

The results of the research showed that when the freely dissolved concentrations of PAHs were kept constant, the effect of suspended particles on PAH bioaccumulation in zebrafish was due to that the PAHs associated with particles were partly bioavailable, and the particle-associated PAHs could be ingested by zebrafish. Part of the PAHs associated with the particles in the digestive tract would be desorbed by the effect of digestive juice, and then absorbed by the zebrafish. The desorption of particle-associated PAHs was related with the characters of the particles, such as the size and composition of the particle. In this research, the smaller grain sizes of SPS exhibited much more stronger effect on the bioaccumulation of PAHs by zebrafish, and this was probably due to their lower organic carbon content, lower ratio of black carbon to organic carbon content, smaller particle size, and higher dissolved organic matter contents, which could promote the desorption of PAHs from the smaller size particles, and increased the bioaccessibility of PAHs to the zebrafish. In addition, PAHs associated with particles will continuously contact with the gills when zebrafish breathe in water, and the PAHs weakly adsorbed on SPS surface could be released rapidly and accumulated by zebrafish through gills; and this may be another reason that caused the smaller size particles had stronger effect on PAH bioaccumulation in zebrafish.

The findings obtained from this study indicate that PAHs on suspended particles are partly bioavailable to zebrafish, and particle ingestion is an important route in PAH bioaccumulation. The effect of SPS on PAH bioaccumulation is not only related with suspended particle concentrations, but also with the size as well as the composition of the particles. This study suggests that the concentrations, particle sizes, and compositions of the SPS should all be considered in ecological risk assessment for the bioavailability of HOCs associated with SPS in aquatic environment.