The presence of arsenic (As) in the sediment and the particulate and dissolved fractions of the water column determines its behavior and bioavailability. The main geochemical parameters responsible for As mobility are organic matter and oxide-forming metals such as Fe. The As distribution and its concentration were evaluated in the dissolved fraction, suspended particulate matter (SPM) and sediment of the lower Paraíba do Sul River (PSR), its main tributaries (Muriaé, Pomba, and Dois Rios rivers), and flooded and estuarine areas. As was not detected in the dissolved fraction. The river flow influenced the As concentration in the SPM, which was higher in the dry season than in the rainy season (2.6 ± 0.69 and 1.98 ± 0.29 mg kg⁻¹, respectively). The Fe oxyhydroxides, organic carbon, and surface area measured in the sediment were positively related with As concentration (R² = 0.11, 0.34, and 0.30; p < 0.05). The highest As concentrations in the sediment occurred in the secondary estuary and flooded areas (5.16 ± 4.78 and 1.23 ± 0.44 mg kg⁻¹, respectively), in which finer granulometric fractions (silt and clay) predominated (64% and 71%, respectively), in addition to greater surface area. The measurement of stable carbon and nitrogen isotopes (δ¹³C and δ¹⁵N) and atomic ratio (C:N)a indicated the existence of a combination of autochthonous and allochthonous sources of organic matter composing the SPM. In general, the As concentrations in the sediment and SPM were low, with values below that permitted by Brazilian regulations (5.9 mg kg⁻¹), which suggests that the As sources in the lower basin of the PSR are diffuse and natural.

沉积物中砷（As）的存在以及水柱中的颗粒物和溶解物决定了它的行为和生物利用度。造成As迁移的主要地球化学参数是有机物和形成氧化物的金属，例如Fe。评估了南帕拉伊巴河（PSR），其主要支流（穆里埃河，庞巴河和多伊斯里奥斯河）的溶解度，悬浮颗粒物（SPM）和沉积物中的砷分布及其浓度，以及洪水和河口地区。在溶解级分中未检测到。河流流量影响了SPM中的As浓度，干旱季节的雨水含量高于雨季（2.6±0.69和1.98±0.29 mg kg ^-1）， 分别）。沉积物中测得的氢氧化铁，有机碳和表面积与砷浓度呈正相关（R ² = 0.11、0.34和0.30；p <0.05）。沉积物中最高的As浓度发生在次生河口和洪水区（分别为5.16±4.78和1.23±0.44 mg kg ^-1），其中较细的颗粒级分（粉砂和粘土）占主导地位（分别为64％和71％） ），更大的表面积。稳定碳和氮的同位素的测量（δ ¹³ C和δ ¹⁵ N）和原子比（C：N）一指出存在组成SPM的有机物的外源和外源的组合。通常，沉积物和SPM中的As浓度较低，其值低于巴西法规所允许的浓度（5.9 mg kg ^-1），这表明PSR下部盆地中的As源是分散的和自然的。