Natural dissolved organic matter (DOM) in groundwater plays a crucial role in mobilizing arsenic (As). The complex contribution of DOM sources makes it hard to predict how the variation of environmental conditions would affect the distribution of As concentrations. Identifying the carbon isotope fractionation of DOM is the key to quantify DOM sources based on stable carbon isotopes. To understand the magnitude and variability in the carbon isotopic fractionation of DOM in competitive adsorption with As(V), this study investigated the δ¹³C values of fulvic acid (FA) and DOM during adsorption to goethite in the presence of As(V), at a specific pH and temperature. The carbon isotopic enrichment factor (ε) of FA in the adsorption to goethite was 0.65 ± 2.11‰ at pH 4.1, 25 °C, suggesting that FA molecules containing ¹³C were more easily adsorbed to goethite. An increasing temperature increased ε_FA from 0.32 ± 1.17‰ to 0.82 ± 5.39‰ at 15–35 °C. For dissolved sediment organic matter (DSOM) cases, molecules containing ¹³C were more easily adsorbed to goethite. However, enrichment factors were not detected due to a reduction in DSOM adsorption and the diversity of natural humic substances or groups. The findings provide basic data for accurately ascertaining DOM sources through carbon isotopes, which is significant for predicting As fluctuation in aquifers affected by monsoon climate and/or human activities.

地下水中的天然溶解有机物（DOM）在调集砷（As）中起着至关重要的作用。DOM来源的复杂贡献使得很难预测环境条件的变化将如何影响As浓度的分布。识别DOM的碳同位素分馏是基于稳定碳同位素定量DOM来源的关键。为了理解在竞争吸附DOM的碳同位素分馏与As（V）的大小和可变性，本研究调查了δ ¹³ Ç吸附期间黄腐酸（FA）和DOM的值，以针铁矿在As的存在（V） ，在特定的pH和温度下。碳同位素富集因子（εpH值为25，温度为4.1时，FA在针铁矿中的吸附为0.65±2.11‰，这表明含¹³ C的FA分子更容易被针铁矿吸附。升高的温度增加ε _FA从0.32±1.17‰至0.82±5.39‰在15-35℃。对于溶解性沉积物有机物（DSOM），含有¹³ C的分子更容易吸附到针铁矿上。但是，由于DSOM吸附的减少以及天然腐殖质或基团的多样性，未检测到富集因子。这些发现为通过碳同位素准确确定DOM来源提供了基础数据，这对于预测受季风气候和/或人类活动影响的含水层中的As波动具有重要意义。