Department of Environmental Science and Analytical Chemistry , Stockholm University , Svante Arrhenius väg 8 , SE-106 91 Stockholm , Sweden.
Mass Spectrometry Laboratory , Center for Physical Science and Technology , Savanoriu 231 , LT-02300 Vilnius , Lithuania.
Environ Sci Technol. 2018 Apr 17;52(8):4861-4868. doi: 10.1021/acs.est.7b05782. Epub 2018 Mar 29.
Stable nitrogen isotopes (δN) are used as indicators of trophic position (TP) of consumers. Deriving TP from δN of individual amino acids (AAs) is becoming popular in ecological studies, because of lower uncertainty than TP based on bulk δN (TP). This method would also facilitate biomagnification studies provided that isotope fractionation is unaffected by toxic exposure. We compared TP and TP estimates for a sediment-dwelling bivalve from two coastal sites, a pristine and a contaminated. Chemical analysis of PCB levels in mussels, sediments, and pore water confirmed the expected difference between sites. Both methods, but in particular the TP underestimated the actual TP of bivalves. Using error propagation, the total uncertainty related to the analytical precision and assumptions in the TP calculations was found to be similar between the two methods. Interestingly, the significantly higher intercept for the regression between TP and TP in the contaminated site compared to the pristine site indicates a higher deamination rate due to detoxification as a result of chronic exposure and a higher N fractionation. Hence, there is a need for controlled experiments on assumptions underlying amino acid-specific stable isotope methods in food web and bimagnification studies.
稳定氮同位素 (δN) 被用作消费者营养位置 (TP) 的指标。由于基于大量 δN 的 TP (TP) 的不确定性较低，因此从个别氨基酸 (AA) 的 δN 中得出 TP 变得越来越流行。这种方法还将促进生物放大研究，只要同位素分馏不受有毒暴露的影响。我们比较了来自两个沿海地点的一种底栖双壳类动物的 TP 和 TP 估计值，一个是原始的，一个是受污染的。贻贝、沉积物和孔隙水中 PCB 水平的化学分析证实了两个地点之间的预期差异。两种方法，但特别是 TP 低估了双壳类动物的实际 TP。通过误差传播，发现两种方法中与 TP 计算的分析精度和假设相关的总不确定性相似。有趣的是，与原始站点相比，污染站点中 TP 与 TP 之间的回归截距显着更高，这表明由于慢性暴露导致的解毒作用，脱氨率更高，N 分馏更高。因此，需要在食物网和双放大研究中对基于氨基酸的稳定同位素方法的假设进行对照实验。
