|Place of Conferral||中国科学院海洋研究所|
为探究自然海域浮游动物摄食微塑料的情况，本论文首次研究了南海北部5个浮游动物类群（桡足类、毛颚类、水母、虾类和仔稚鱼），并且比较了大型浮游生物网（简称网I，筛绢规格505 μm）和中型浮游生物网（简称网II，筛绢规格160 μm）样品的分析结果。在16个采样站位的浮游动物中均检测到微塑料的存在，其中纤维状微塑料所占的比例最大（70%），其次是颗粒状和碎片状。浮游动物体内检出微塑料的主要成分是聚酯。网Ⅰ和网Ⅱ中浮游动物体内微塑料的平均长度分别为125 μm和167 μm。网I中5个浮游动物类群单个浮游动物体内微塑料含量分别为0.05、0.15、0.34、0.49和1.2个/浮游动物，网II中为0.08、0.21、0.47、0.60和1.43个/浮游动物，网II中5个浮游动物类群单个浮游动物体内微塑料含量均高于网I，但是两种网具中也出现了相同的趋势：单个浮游动物体内微塑料含量从桡足类、毛颚类、水母、虾类到仔稚鱼不断增加，即营养级越高，生物摄食微塑料的几率越大。在单个浮游动物体内微塑料含量的基础上，结合每个站位浮游动物丰度，获得浮游动物摄食微塑料的平均丰度，网I为4.1个/m3，网II为131.5个/m3。与单个浮游动物体内微塑料含量随着营养级的升高而增加的趋势相反，由于水母、虾和仔稚鱼等营养级较高的浮游动物的丰度低，其摄入的微塑料总丰度也随之降低。在空间分布上，无论是单个浮游动物体内微塑料含量，还是浮游动物摄食微塑料的总丰度，两种网具的调查结果都是相似的。
为进一步量化浮游动物对微塑料的摄食作用，选取了中国近海浮游动物优势种中华哲水蚤作为实验生物，将中华哲水蚤放置于含有微塑料环境中，设置不同微塑料粒径、浓度和饵料浓度。结果表明，中华哲水蚤在微塑料污染的环境中能够摄食微塑料，中华哲水蚤对微塑料的摄食率会随着微塑料粒径的增大而降低：微塑料粒径为2 μm时平均摄食率为130.6 ± 40.3个/h；粒径为20 μm时平均摄食率为13 ± 6.4个/h；粒径为200 μm时平均摄食率为0.07个/h。在微塑料粒径相同的条件下，中华哲水蚤对微塑料的摄食率随着水体中微塑料浓度的升高而升高，并且体内出现微塑料的中华哲水蚤个体所占比例也会升高。被中华哲水蚤摄入的微塑料不会一直停留在生物体内，会随着粪便排出体外，所以在当水体中无微塑料时，一段时间（最长4.5 h）之后中华哲水蚤能够排出体内所有的微塑料颗粒。长期培养实验结果表明，摄食微塑料对中华哲水蚤存活率不会产生显著效应，但是能够抑制中华哲水蚤的排便速率，造成假饱腹感，降低其捕食效率使中华哲水蚤种群质量下降。另外，如果改变中华哲水蚤的饵料浓度，饵料浓度为104 cells /mL时，中华哲水蚤对微塑料的摄食率最高，饵料浓度偏低或者偏高时摄食率均与之存在显著性差异。
为揭示中国近海鱼类体内的微塑料滞留率和基本特征，本论文在黄海海区设置了53个调查站位，使用底拖网进行鱼类样品采集，系统地研究了19种黄海主要鱼类，19种鱼类中都检测到微塑料。总体来说，34%（444/1320）的鱼体内检测出共 552个塑料，其中546个（99%）粒径< 5 mm，属于微塑料范畴。小黄鱼（Larimichthys polyactis）体内微塑料滞留率最高，单个鱼类体内微塑料数量为0.97；刺鲳（Psenopsis anomala）和银鲳（Pampus argenteus）体内微塑料滞留率最低，单个鱼类体内微塑料数量为0.20。主要分为三种形状：纤维状、颗粒状和碎片状，分别占总数的67%、22%和11%。微塑料长度范围在16–4740 μm之间，平均长度为941 ± 43 μm，其中纤维状、颗粒状和碎片状微塑料的平均长度分别为1233 ± 57 μm、263 ± 24 μm和503 ± 91 μm，微塑料长度与鱼体长度呈正相关。所有微塑料成分组成中包括14种聚合物，其中以有机氧化聚合物（40%）最为丰富，其次是聚乙烯（22%）和聚酰胺（11%）。微塑料在鱼体内的数量受采样海域和鱼体重量的影响。在靠近渤海和长江口附近海域采集的鱼类体内，微塑料含量高于从黄海中部采集的鱼类。如果只关注体内含有微塑料的鱼类个体，则每条鱼体内微塑料数量与鱼体重量呈负相关。摄食微塑料可能会影响黄海渔业资源的质量和数量，特别是具有重要经济价值的鱼类。
为进一步研究确定鱼类对微塑料的摄食率、滞留率和鱼体的成活率，选取了具有重要经济价值的大菱鲆（Scophthalmus maximus）幼鱼作为研究对象进行微塑料暴露实验，培养水体环境中设置不同浓度的微塑料和饵料。结果证明，暴露在含有微塑料的环境中，大菱鲆幼鱼会出现摄食微塑料的现象。饵料浓度的改变对大菱鲆幼鱼摄食微塑料的影响显著，未添加饵料的大菱鲆幼鱼平均每个粪便中含有0.2个微塑料，当饵料浓度为5.5×10-4 g时，粪便中微塑料数量平均为13.4个，但是增加饵料浓度，大菱鲆幼鱼摄食微塑料的数量出现下降趋势。被摄食的微塑料会在大菱鲆幼鱼体内滞留，滞留率与体内微塑料数量和环境中饵料浓度有关，转移到无微塑料环境中24 h后，当饵料浓度为5.5×10-4 g时，大菱鲆幼鱼体内滞留的微塑料数量平均为1.4个，饵料浓度为5.5×10-2和0.55 g时，大菱鲆体内的微塑料则被完全排出体外。另外，实验过程中还发现大菱鲆幼鱼的鳃部也有微塑料出现。大菱鲆鳃部微塑料的数量也受环境中饵料浓度的影响，当环境中饵料浓度为5.5×10-4 g时，平均每条大菱鲆鳃中微塑料数量为3.6个，随着饵料浓度增加，鱼鳃中微塑料数量呈现下降趋势。与对照组相比，微塑料对大菱鲆幼鱼的生长发育影响效果不显著（p > 0.05）。但是摄食微塑料会降低大菱鲆幼鱼的存活率，浓度越高，大菱鲆幼鱼的存活率越低。
Microplastics (MPs) are plastic particles smaller than 5 mm. Microplastics pollution in the environment has become a global problem in the past decades. Due to its widespread occurrence & accumulation and potential threats to marine organisms, it has recently attracted more and more attention. These plastic particles come from a wide range of sources, mainly including processed materials used in industry, plastic fragments from the large plastics broken by physical processes, supplementation of daily necessities, and polishing materials applied in industrial production. If they enter the marine environment, microplastics may exist for a long time, because of their large specific surface area and the accumulation marine microorganisms, they will absorb the surrounding chemical materials (such as heavy metals and persistent organic pollutants (POPs). Ingestion of microplastics can physically and chemically affect marine organisms, and also biologically amplified through the food chain. In this paper, we investigated 5 zooplankton groups and 19 species fish in the South China Sea and the Yellow Sea, respectively. Laboratory experiments have been performed on a variety of marine biota, including copepod Calanus sinicus and turbot Scophthalmus maximus.
For the first time, the ingestion of microplastics of five natural zooplankton groups in the north part of the South China Sea, including copepods, chaetognaths, jellyfish, shrimps, and fish larvae, was studied, and two kinds of sampling nets, Net Ⅰ and Net ⅠⅠ (505 μm and 160 μm in mesh size), were contrasted. The microplastics were detected in zooplankton from 16 stations, of which fiber was the most microplastics of all samples, with a proportion of 70%, followed by particles and fragments. The main chemical component of microplastics detected in zooplankton was polyester. The average sizes of microplastics in Net I and Net II were 125 μm and 167 μm, respectively. The average encounter rates between microplastics and 5 zooplankton groups in Net I were 0.05, 0.15, 0.34, 0.49, and 1.2 pieces/individual, respectively, while in Net II they were 0.08, 0.21, 0.47, 0.60, and 1.43 pieces/individual. The ingestion rate of the five zooplankton groups in Net II was higher than that in Net I, but the trend in the two nets was the same: the encounter rates with microplastics increased from copepods, chaetognaths, jellyfish, shrimps to fish larvae. In other words, the higher the nutrition level, the higher the encounter rate with microplastics. Combined the encounter rate and the abundance of zooplankton in each station, the average abundance of ingested microplastics was 4.1 pieces/m3 for Net I, 131.5 pieces/m3 for Net II. Contrary to the increased trend of encounter rate as trophic levels increase, the total amount of microplastics consumed by zooplankton with higher trophic level (such as jellyfish, shrimp, and fish larvae) has decreased. As far as spatial distribution is concerned, the encounter rates with microplastics or the abundance of ingested microplastics in the two nets are similar.
In order to further verify the feeding effect of zooplankton on microplastics, we selected the dominant zooplankton species, Calanus sinicus, as the experimental organism, and carried out indoor microplastics exposure experiment with different particle sizes, concentrations of microplastics and feeding concentrations. The results show that the feeding rate of copepod Calanus sinicus on microplastics decreased with the increase of microplastics particle size. When the particle sizes were 2 μm, 20 μm, and 200 μm, the average ingestion rates of microplastics were 130.6 ± 40.3 pieces/h, 13 ± 6.4 pieces/h, and 0.07 pieces/h, respectively. When more microplastics were present in the environment, both the feeding rate and the proportion of individuals with microplastic increased. Microplastics, ingested by the copepod, can be excreted together with feces. Therefore, once copepod was transferred to the water with no microplastics, the copepod can expel all microplastics in their digestive tract within 4.5 h. The results of long-term culture showed that microplastics had no significant effect on the survival rate of the copepod, but it can inhibit their defecation rate, cause false satiety, and reduce the efficiency of predation and the population quality of the copepod.
As an important seafood, fish can provide human with protein and raw materials of pharmaceutical industry, however, fish living in coastal environments are easy to ingest microplastics, and the research on fish with microplastics in China’s coastal is very limited. We investigated the characteristics and retention rate of microplastics in fish collected from the Yellow Sea in 53 sites by bottom trawl. All 19 species contained microplastics. Typically, 34% (444 / 1320) fish retained plastics pellets, and 552 pieces plastics pellets were removed from the fish, of which 546 (99%) were microplastics (size < 5 mm). The retention rate of microplastics in Larimichthys polyactis was the highest (0.97 MP/fish for all fish). Psenopsis anomala and Pampus argenteus contained 0.20 MP/fish for all fish, which was the lowest retention rate among 19 species. These microplastics were divided into three shapes: fibers, pellets, and fragmented, accounting for 67%, 22%, and 11% of the total, respectively. The length of microplastics ranged from 16–4740μm with an average length of 941μm. In all microplastics, the average lengths of the fibers, pellets, and fragments were 1233 ± 57 mm, 263 ± 24 mm, and 503 ± 91 mm. There was a positive correlation between the length of microplastic and the length of fish body. There are 14 polymers in the composition of all microplastics, the most abundant of which are organic oxidation polymers (40%), followed by polyethylene (22%) and polyamide (11%). The retention rate of microplastics ingested by fish was affected by the sea area sampled and fish weight. The content of microplastics in the fish collected near the Bohai Sea and the Yangtze River Estuary was higher than that in the fish collected from the middle of the Yellow Sea. If we only focus on the individual fish with microplastics, the amount of microplastics in each fish is negatively related to the weight of the fish. Ingestion of microplastics may affect the quantity and the quality of fishery resources in the Yellow Sea, especially species with major economic value.
To further study the ingestion rate of microplastics, retention rate, and survival rate of fish as well as to make a reasonable risk assessment based on the field results, we selected turbot juveniles as the experimental organism exposed to different concentrations of microplastics and baits. The results showed that when exposed to the environment containing microplastics, the turbot juveniles would ingest microplastics. Feeding concentration had a significant effect on the consumption of microplastics by turbot juveniles (p < 0.05). When the food and microplastics present in the environment at the same time, the amount of microplastics in the feces of turbot juveniles was high when the food concentration was low; on the contrary, if the food concentration was relatively high, the amount of microplastics in the feces of turbot juveniles was low, or even no microplastics. The average amount of microplastics in the feces of juvenile turbot without food was 0.2. When the feeding concentration was 5.5×10-4 g/fish, the average amount of microplastics in the feces was 13.4 pieces/feces. The retention rate was related to the amount of microplastics in the body and the concentration of food in the environment. When the feeding concentration was 5.5×10-4 g/fish, the average amount of microplastics in the body of turbot was 1.4 pieces/feces, and when the feeding concentration was 5.5×10-2 and 0.55 g/fish, the microplastics in the body of turbot were completely discharged from the body. In addition, microplastics were found in gills of juvenile turbo, which affected by the concentration of food in the environment. The amount of microplastics in gills decreased with the increased food concentration. When the feed concentration in the environment was 5.5×10-4 g/fish, the average number of microplastics in each gill of turbot was 3.6 pieces/feces. Compared with the control group, the effect of microplastics on the growth and development of turbot larvae was not significant (p > 0.05). However, high concentration of microplastics reduced the survival rate of turbot juveniles.
Based on the research results of this paper, we have come to the following conclusions: (1) microplastics was detected in the body from zooplanktons and fish; (2) zooplankton groups in higher trophic level contained more microplastics than that in lower trophic level; (3) the main shape and composition of microplastics in marine organisms was fibre and organic oxidation polymer; (4) microplastics could affect the feeding rate and excretion rate of zooplankton and fish, reduce their survival rate, which indicated that China's coastal organisms were threatened by microplastics. The results of our study will provide basic data and theoretical basis for further assessment of the risk of ecosystem and fishery resources in coastal waters in China.
|李庆洁. 海洋浮游动物及鱼类对微塑料的摄食研究[D]. 中国科学院海洋研究所. 中国科学院大学,2020.|
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