# Derivation of a Freshwater Quality Benchmark and an Ecological Risk Assessment of Ferric Iron in China

## TL;DR

This study establishes freshwater quality benchmarks for ferric iron in China and finds significant ecological risks in several river basins.

## Contribution

The paper provides novel freshwater quality benchmarks and ecological risk assessments for ferric iron in China.

## Key findings

- 30% of acute and 83% of chronic risk quotients indicate ecological risks in Chinese river basins.
- Yellow River, Huaihe, and Songhua-Liaohe basins show the highest risk.
- Acute HC5 is 689 μg/L and SWQC is 345 μg/L for ferric iron.

## Abstract

Acid drainage resulting from mining operations has led to significant iron contamination in surface waters, posing serious ecological and public health hazards. Elevated iron levels in freshwater ecosystems can severely affect aquatic organisms and human health. However, there remains a considerable gap in the establishment of benchmark values and ecological risk assessments (ERAs) for iron in surface waters in China. This study collected and screened 47 acute and chronic toxicity data points of 22 species for ferric iron (Fe3+) from various studies and databases. Three widely utilized methodologies were applied to derive long-term and short-term water quality criteria (LWQC and SWQC, respectively) for Fe3+; the logistic fitting curve based on the species sensitivity distribution (SSD) method was identified as the most optimal method, yielding an acute HC5 of 689 μg/L and an SWQC of 345 μg/L. The LWQC of Fe3+ was estimated to be 28 μg/L by dividing HC5 by the acute-to-chronic ratio (ACR), owing to the inadequacy of chronic toxicity data for model fitting. Utilizing these benchmarks, an ecological risk assessment (ERA) was conducted to compare the benchmarks with 68 iron exposure data points collected from surface waters across 30 provinces from eight river basins of China. The findings of 30% of the acute risk quotients and 83% of the chronic risk quotients raise substantial ecological concerns, primarily regarding the Yellow River Basin, Huaihe River Basin, and Songhua and Liaohe River Basin. This research provides critical insights into Fe3+ toxicity data collection and benchmark derivations, offering a benchmark data foundation for the remediation of surface water iron contamination and water quality management in China.