Abstract: Some of rivers on the Qinghai-Tibet Plateau have high dissolved arsenic (As) levels, posing a potential threat to the health of local residents. To identify the sources and natural attenuation of dissolved As in the rivers, we analyzed the dissolved As concentrations in 11 river water samples, 3 hot spring samples, 2 lake water samples, and 1 rainwater sample collected from the Dogxung Zangbu River. Results showed that As concentration in the hot spring samples was up to more than 9000 μg·L^-1. The As concentrations in the two lake water samples were 14.1 and 93.8 μg·L^-1, respectively. The As concentrations of river samples ranged from 0.83 to 177 μg·L^-1 (mean 45.5 μg·L^-1), with 64% of the samples exceeding 10 μg·L^-1. The As concentration of rainwater sample was below 0.1 μg·L^-1. The As-rich hot springs were an important source of dissolved As in river water, while other sources contributed less. From upstream to downstream, dilution, adsorption, and co-precipitation of As by river suspended matter or sediments are important processes for the natural attenuation of dissolved As in river water. These As-enriched river suspended matters or sediments are transported downstream and deposition, which may lead to high As levels in sediments and groundwater in downstream regions, thus affecting the drinking water safety of local residents.

Key words: Qinghai-Tibet Plateau, river water, arsenic, hot spring