Evaluating water quality and ecotoxicology assessment techniques using data from a lead and zinc effected upland limestone catchment

Abstract

Point and diffuse sources associated with historical metal ore mining are major causes of metal pollution. The understanding of metal behaviour and fate has been improved by the integration of water chemistry, metal availability and toxicity. Efforts have been devoted to the development of efficient methods of assessing and managing the risk posed by metals to aquatic life and meeting national water quality standards. This study focuses on the evaluation of current water quality and ecotoxicology techniques for the metal assessment of an upland limestone catchment located within a historical metal (lead ore) mining area in northern England. Within this catchment, metal toxicity occurs at circumneutral pH (6.2-7.5). Environmental Quality Standards (EQSs) based on a simple single concentration approach like hardness based EQS (EQS-H) are more overprotective, and from sixteen sites monitored in this study more than twelve sites (>75%) failed the EQSs for Zn and Pb. By increasing the complexity of assessment tools (e.g. bioavailability-based (EQS-B) and WHAM-F), less conservative limits were provided, decreasing the number of sites with predicted ecological risk to seven (44%). Thus, this research supports the use of bioavailability-based approaches and their applicability for future metal risk assessments.

Effect of episodic rainfall on aqueous metal mobility from historical mine sites

“…In addition, toxicity of metal mixtures including protons (H þ ) and metals (Al 3þ , Zn 2þ , Pb 2þ and Cu 2þ ) was estimated using WHAM-F TOX. [33] Procedures for WHAM/Model VII and WHAM-F TOX were followed as described in Valencia-Avellan et al, [23] detailed in the Supplementary material.…”

“…Results are compared with those obtained from a previous comprehensive annual analysis of monthly surveys under non-episodic conditions. [22,23] From this assessment, the mobilisation and potential toxicity of dissolved metals under flow conditions derived from episodic rainfall will provide important information regarding key rainfall-induced processes in the behaviour of pollutant metals, supporting future risk mitigation strategies in similar catchments.…”

“…[21] For example, where rivers flow over limestone bedrock, the pH is buffered, exerting controls over mineral solubility, metal transport and bioavailability. [22,23] However, rainfall (e.g. acid rain) may produce shifts in the pH, affecting the buffering capacity of the river chemistry, allowing desorption of metals from sediments or soils.…”

“…The catchment chemistry has previously been characterised [22] and assessed with respect to water quality and ecotoxicology under seasonal conditions. [23] Three sampling stations were selected for the present study: an ephemeral tributary (ET) located in the most upstream zone, draining an area of mine spoil wastes; a perennial tributary (PT) of an underground mine channel located in middle of the stream; and a site located downstream on the main channel (MC) 2.27 km from the River Wharfe confluence and adjacent to a flow gauging station (Table S1, available as Supplementary material). Higher metal concentrations in upstream reaches may tend to be diluted by inputs from non-affected tributaries lower down the catchment; however, inputs from mine adits will also have an effect, depending on their chemical characteristics.…”

Trace metal speciation in a wastewater wetland and its bioaccumulation in tilapia Oreochromis niloticus

“…Nevertheless, it is necessary to determine the amounts of the metal species to accurately establish their toxicity or the dynamics occurring at each site [23].…”