Fractionation of Fulvic Acid by Iron and Aluminum Oxides—Influence on Copper Toxicity to Ceriodaphnia dubia

Abstract

This study examines the effect on aquatic copper toxicity of the chemical fractionation of fulvic acid (FA) that results from its association with iron and aluminum oxyhydroxide precipitates. Fractionated and unfractionated FAs obtained from streamwater and suspended sediment were utilized in acute Cu toxicity tests on Ceriodaphnia dubia. Toxicity test results with equal FA concentrations (6 mg FA/L) show that the fractionated dissolved FA was 3 times less effective at reducing Cu toxicity (EC50 13 ± 0.6 μg Cu/L) than were the unfractionated dissolved FAs (EC50 39 ± 0.4 and 41 ± 1.2 μg Cu/L). The fractionation is a consequence of preferential sorption of molecules having strong metal-binding (more aromatic) moieties to precipitating Fe- and Al-rich oxyhydroxides, causing the remaining dissolved FA to be depleted in these functional groups. As a result, there is more bioavailable dissolved Cu in the water and hence greater potential for Cu toxicity to aquatic organisms. In predicting Cu toxicity, biotic ligand models (BLMs) take into account dissolved organic carbon (DOC) concentration; however, unless DOC characteristics are accounted for, model predictions can underestimate acute Cu toxicity for water containing fractionated dissolved FA. This may have implications for water-quality criteria in systems containing Fe- and Al-rich sediment, and in mined and mineralized areas in particular. Optical measurements, such as specific ultraviolet absorbance at 254 nm (SUVA254), show promise for use as spectral indicators of DOC chemical fractionation and inferred increased Cu toxicity.

The influence of the quantity and quality of sediment organic matter on the potential mobility and toxicity of trace elements in bottom sediment

“…The content of dissolved organic carbon (DOC) is an important indicator when characterising bottom sediments due to its high significance in the assessment of water quality. DOC is considered to be a mobile, available and ecologically important fraction of organic matter in the bottom sediments (Akkanen et al 2005; Smith et al 2014). The content of DOC in the studied bottom sediments was on average 0.44 g/kg s.m., which was less than 1% of the TOC content (Table 1).…”

“…On the other hand, different fractions of organic matter are known to regulate the behaviour of trace elements in the water ecosystem (Calace et al 2006; Yang et al 2011). The interactions of trace elements with a variety of organic substances (fulvic acid, humic acid, non-hydrolysing carbon, DOC) play an important role in the distribution, bioavailability and protection of aquatic organisms against the toxicity of an excessive content of trace elements (De Schamphelaere et al 2005; Yang et al 2011; Fonseca et al 2013; Smith et al 2014; Bai et al 2018). Trace elements bound on humic substance are relatively immobile, and the functional groups: carboxylic (–COOH), phenolic (–OH) and amino acid residues (amine, amide, sulphur groups) are mainly involved in the formation of element-humic complexes; however, this sorption behaviour is strongly impacted by the pH and ionic strength (Smith et al 2014; Boguta and Sokołowska 2016; Bai et al 2018).…”

“…The behaviour of trace elements in bottom sediments is controlled by many factors, such as: pH, redox condition, temperature, electric conductivity, content of the clay fraction, content of iron and manganese oxides and the form of elements (Singh et al 2005; Fonseca et al 2013; Cao et al 2015; Martínez-Santos et al 2015). However, the content and quality of organic matter play a very important role in the assessment of trace element behaviour in the aquatic environment (Filcheva and Yurukova 2004; Hristov et al 2009; Yang et al 2011; Smith et al 2014; Smal et al 2015; Derrien et al 2017). The organic matter of bottom sediments is subjected to various processes, which may affect its character in a relatively short period of time, leading to the creation of humic compounds that are active in reactions with trace elements (Derrien et al 2017).…”

Soft and sour: The challenge of setting environmental quality standards for bioavailable metal concentration in Fennoscandinavian freshwaters

“…Therefore, the Zn EQS and LC 50 decrease with increasing pH or are pH insensitive at medium to high Ca concentrations (Fig. 5) (Tipping et al, 2002;Smith et al, 2014). Soft waters have gained attention in the EU risk assessment report for zinc where a special soft water PNEC value was derived (JRC-IHCP, 2010).…”

Understanding Organic Nonpoint‐Source Pollution in Watersheds via Pollutant Indicators, Disinfection By‐Product Precursor Predictors, and Composition of Dissolved Organic Matter

“…These pollutants enter waterways adjacent to drainage systems, either directly or in runoff or seepage, accumulate along waterways, and ultimately contribute a great load of dissolved organic matter to downstream watersheds or lakes (Hosen et al, 2014). Dissolved organic matter elevates organic pollution indicators, contributes to unpleasant odors and colors, and can interact with metals via complexation (Ohno et al, 2008; Yu et al, 2012; Orsetti et al, 2013; Yacob et al, 2013; Chen et al, 2015; Mladenov et al, 2015), competitive sorption (Smith et al, 2014; Mladenov et al, 2015), and electron shuttling (Mladenov et al, 2010, 2015).…”