长江口底层水中有机锡赋存特征及其在低氧区的行为

Occurrence of Organotin in Bottom Water of the Yangtze River Estuary and Its Behavior in the Seasonally Hypoxic Zone

摘要:

2019年夏季在长江口―东海海域纵向断面上进行现场采样和观测，获取了12个走航站位和低氧区1个连续测站的水质数据和24个底层水样，样品经过滤、固相萃取和乙基化衍生等处理后利用气相色谱?质谱联用仪检测了9种有机锡化合物浓度，旨在分析其在长江口海域的空间分布和潮汐变化特征，并探索其在口外低氧区的行为。结果表明，在长江口海域底层水体中溶解态有机锡质量浓度范围为33.9 ~ 203 ng?L^-1 （以Sn计， 以下同），平均值为125 ng?L^-1；仅有42%样品检出三丁基锡（TBT），其质量浓度最高可达53.1 ng?L^-1，其余8种有机锡化合物检出率可达92%~100%。其中，甲基锡类质量浓度为（36.7 ± 16.2）ng?L^-1，约占溶解态有机锡质量浓度的20% ~ 40%；丁基锡类质量浓度为（33.1 ± 22.0）ng?L^-1，约占溶解态有机锡质量浓度的16% ~ 45%；苯基锡类质量浓度为（55.7 ± 12.4）ng?L^-1，约占溶解态有机锡质量浓度的26% ~ 59%。在河口最大浑浊带和口外低氧区，以及低氧区的涨潮流向落潮流转换阶段，底层水出现溶解态有机锡的质量浓度峰值，主要增加的是TBT及一取代有机锡化合物。研究还发现，三苯基锡（TPhT）和一丁基锡（MBT）质量浓度随溶解氧饱和度降低而增加。潮汐影响下底边界层中的再悬浮和还原溶解过程，导致底层水中的TBT和TPhT等有机锡呈现脉冲式暴露，其生态风险值得进一步关注和研究。

Abstract:

In the summer of 2019， field sampling and observation were conducted at 12 sites and one anchor station （at the seasonally hypoxic zone） along a longitudinal section from the Yangtze River （Changjiang） estuary to the East China Sea. The water quality data in the vertical profile and bottom water samples were collected. After sample filtration， solid phase extraction and ethylating derivatization， the concentrations of nine organotin compounds were detected by gas chromatography-mass spectrometry. The purpose of this study was to analyze its spatial distribution and tidal variation in the Yangtze River estuary， and to explore its behavior in the low oxygen area outside the estuary. The results show that the concentrations of dissolved organotin in the bottom water of the Yangtze River Estuary ranges from 33.9 to 203 ng?L^-1 （as Sn）， with an average of 125 ng?L^-1. Tributyltin （TBT） is detected in only 42% of the samples， and the highest concentration of TBT is 53.1 ng?L^-1. The detection rates of the other eight organotin compounds were 92% to 100%. The methyltin concentrations are （36.7 ± 16.2） ng?L^-1， accounting for 20% to 40% of the total concentrations of dissolved organotin species. The concentrations of butyltin are （33.1 ± 22.0） ng?L^-1， accounting for about 16% to 45%. The concentrations of phenyltin are （55.7 ± 12.4） ng?L^-1， accounting for about 26% to 59%. In the estuarine turbidity maximum zone and the coastal seasonally hypoxic zone， as well as in the tidal transition stage from flood tide to ebb tide， the concentrations of dissolved organotin species in bottom water peak， which is mainly attributed to the increase of dissolved TBT and mono-substituted organotin compounds. It is also found that the concentrations of triphenyltin （TPhT） and monobutyltin （MBT） increase with the decrease of dissolved oxygen saturation. The tide-driven resuspension and reductive dissolution in the bottom boundary layer lead to pulsed exposure of organotin such as TBT and TPhT in the bottom water， which may pose ecological risk to marine benthos and deserves further attention and research.