Metal contamination of bed sediments in the Irwell and Upper Mersey catchments, northwest England: exploring the legacy of industry and urban growth

Abstract

Purpose Manchester is often heralded as the first industrial city. Large volumes of physical and liquid contaminants were released into its river network throughout the industrial period up to the latter part of the twentieth century. Water quality has improved dramatically in recent decades, but, given their environmental significance, it is important to ascertain the extent to which a legacy of contamination persists in the modern bed sediments. Materials and methods Fine-grained bed sediments were sampled at 40 sites in the Mersey and Irwell catchments. Sediments were wet sieved to isolate the <63-μm grain size fraction. Metal concentrations were determined using XRF. Particle size characteristics were also measured. Sediments were subjected to a five-step sequential extraction procedure to ascertain the environmental significance of metal concentrations. Alongside archival research of past industry, enrichment factors, multivariate statistical techniques and conditional inferences trees were used to identify sources of heavy metals. Results and discussion Bed sediment-associated heavy metal(-loid) concentrations were as follows: As (9.89-110 mg kg −1 ), Cr (76.5-413 mg kg −1 ), Cu (53.1-383 mg kg −1 ), Pb (80.4-442 mg kg −1 ) and Zn (282-1020 mg kg −1 ). Enrichment factors ranged from moderate to extremely severe, with Pb showing the greatest enrichment across the catchments. Chemical mobility was generally low, but metal(loid) partitioning identified the influence of anthropogenic sources. Statistical analysis highlighted a number of point sources associated with former industrial sites that operated during the industrial period. Conditional inference trees highlighted the role of the textile industry on Cu concentrations in addition to indicating the complexity of sources, fluxes and stores of sediment-associated contamination throughout the system. Conclusions Fine-grained sediment-associated metal(loid)s in the Mersey and Irwell catchments are anthropogenically enriched. Concentrations also exceed sediment quality guidelines. A lack of distinct spatial patterning points to a complex network of contaminant inputs across the catchments, even in the headwaters. Whilst potential modern urban sources are likely to be important, spatial patterns and multivariate/data mining techniques also highlighted the importance of releases from former industrial sites as well as the reworking of historically contaminated floodplains and soils.

Highly conservative behaviour of bed sediment‐associated metals following extreme flooding

“…Moreover, there are no significant differences within the upper Mersey and Irwell catchments, and the spatial patterning remains remarkably similar across the entire study area. The distribution of pre‐flooding bed sediment‐associated metal(loid)s and their potential sources are discussed in the study of Hurley et al (). Hurley et al () also compared pre‐flooding values with available sediment quality guidelines.…”

“…The distribution of pre‐flooding bed sediment‐associated metal(loid)s and their potential sources are discussed in the study of Hurley et al (). Hurley et al () also compared pre‐flooding values with available sediment quality guidelines. The post‐flooding concentrations do not alter the original assessment, where all sites exceed threshold and probable effects levels for all of the selected metal (loids) for both Canadian and draft U.K. sediment quality guidelines (CCME, ; Hudson‐Edwards, Macklin, Brewer, & Dennis, ).…”

“…A potentially important mechanism contributing to this limited response might be the significant contamination of headwater systems during the industrial period. Much of the early industry in Manchester was concentrated in upstream reaches to utilise stream flows for water power and capture the “cleaner” waters for processes such as textile bleaching and dyeing (Hurley et al, ). Disposal of physical and chemical waste directly into river channels during the 19th and early 20th century is likely to have produced a network of contaminated floodplain environments in headwater catchments.…”

“…This study builds upon an initial assessment of bed sediment quality in the Irwell and upper Mersey catchments (Hurley, Rothwell, & Woodward, ), and we have focused on the same five anthropogenically enriched metal(loid)s: As, Cr, Cu, Pb, and Zn. Concentrations were measured following an identical analytical procedure using XRF analysis with ICP‐MS calibration.…”

Preface

“…The River Mersey drains the historical industrial cities of Liverpool and Manchester, as well as numerous other smaller towns and cities, and papers in this special issue highlight the persistent nature of trace metals in this region. Hurley et al (2017) investigated sediment quality across the Upper Mersey and Irwell catchments. Despite recent improvements in water quality, there remains widespread contamination of river sediment with trace metals and metalloids (e.g.…”