Hospital Effluent as a New Source of Anthropogenic Lanthanum in the Environment

Abstract

Excess gadolinium (Gd) in the environment, originating from Gd-chelating contrast agents present in hospital wastewater, has been extensively studied as a micropollutant. However, the source of excessive lanthanum (La) levels in the environment remains unclear. In this study, we analyzed rare earth elements (REEs) in treated water from 12 wastewater treatment plants (WWTPs) and sewage sludge/incinerated ash from two sludge treatment centers in Sapporo, Japan, during 2019–2020. We found that the annual discharge of excess Gd and La in a treatment area positively correlated with the number of hospitals in that area. The excess Gd concentration in the treated water increased by an order of magnitude late at night Monday, whereas the excess La concentration remained constant. Sequential extraction experiments on sewage sludge revealed that excess La is predominantly incorporated in phosphate, not silicate, as in zeolite catalysts. We identified lanthanum carbonate tablets (e.g., Fosrenol), prescribed daily to kidney patients to prevent hyperphosphatemia, as the source of excess La. Due to its low solubility, most of the anthropogenic lanthanum settles as sewage sludge in WWTPs, and only a small percentage is released into treated water. This raises concerns about the potential degradation of natural REE patterns in the environment.