Christopher McRae

Effect of groundwater fulvic acid on the adsorption of arsenate by ferrihydrite and gibbsite

Abstract Adsorption studies have been conducted at pH 4, 6 and 8 to assess the effect of fulvic acid on arsenate adsorption to ferrihydrite and gibbsite. The studies compared the adsorption of arsenate on the mineral surfaces in the absence of fulvic acid, to those cases where increasing concentrations of fulvic acid (0.3–60 μM) were added to the mineral–arsenate suspensions. Experiments where arsenate was added to mineral–fulvate suspensions were also conducted. The results suggest that arsenate adsorption on both gibbsite and ferrihydrite decreases with increasing concentrations of fulvic acid. This effect was highest at pH 4, and decreased at pH 6 and 8. Ferrous ion concentrations were very low during the ferrihydrite experiments and support the view that fulvic acid can both displace arsenate from and inhibited its adsorption to mineral surfaces. The experiments also indicated that the amount of arsenate adsorbed was lower if fulvic acid was added before rather than after arsenate. This may reflect the relative size of arsenate and fulvic acid molecules and their ability to penetrate the crystal matrices of the minerals.

The occurrence of methyl, ethyl, propyl, and butyl parabens in the urban rivers and stormwaters of Sydney, Australia

Parabens, commonly used preservatives, are emerging pollutants that are known to enter waterways through the wastewater system where they can pose a threat to aquatic organisms. Less is known about their presence and contribution to urban waterways in cities with separated stormwater and wastewater systems, such as Sydney, Australia. We measured the occurrence of methyl-(MeP), ethyl-(EtP), propyl-(PrP) and butyl-(BuP) parabens in urban river and stormwater samples across a range of land uses, using solid-phase microextraction with gas chromatography-mass spectrometry for the analysis. MeP in modified stormwater channels was more frequently detected and found at higher mean levels (6.29 μg L−1) than in urban rivers (3.62 μg L−1). Waterways in residential catchments had greater mean total paraben load (26.87 μg L−1) when compared to parkland catchments (12.71 μg L−1) and bushland catchments (2.10 μg L−1). EtP had the highest peak concentrations across the study area (max = 305.55 μg L−1) associated with industrial land uses and areas historically associated with poor water quality. The levels of EtP were relatively high when compared to international studies in cities with combined stormwater and wastewater systems. The results also suggest overflows from the sewer during heavy rain are likely not as significant when compared to the contribution from urban runoff. The study did not reveal the source of the EtP and further studies are recommended to identify this and the potential environmental impact.

A comparative structural study of nitrogen-rich fulvic acids from various Antarctic lakes

Environmental context Fulvic acids are important naturally occurring organic materials, but unravelling their complex structures remains challenging. This paper suggests chemical analyses to facilitate structural studies of fulvic acids, and to investigate the similarities and differences of fulvic acids from various natural sources. Abstract We comprehensively examined fulvic acids isolated from three lakes in Vestfold Hills, eastern Antarctica and microbial reference fulvic acid from Pony Lake located in western Antarctica. These fulvic acids were compared in terms of their structural similarities and differences by means of elemental analysis, cross polarisation magic-angle spinning (CP-MAS) 13C NMR spectroscopy, X-ray photoelectron spectroscopy (XPS) and tetramethylammonium hydroxide (TMAH) thermochemolysis coupled to gas chromatography–mass spectrometry (GC-MS). The results indicate that these Antarctic fulvic acids show notable differences in chemical composition and structure; in particular XPS demonstrates that the distribution of nitrogen-containing compounds in the nitrogen-rich Antarctic fulvic acids differ significantly from each other. The dissimilarities are also highlighted in terms of quantity and quality of their nitrogenous constituents. For instance, Organic Lake Fulvic Acid (OLFA) contains around 10 times lower amide groups (pyrimidine–peptide N) than Pendant Lake Fulvic Acid (PNFA). It also shows 1.5 times less quaternary amine than Mossel Lake Fulvic Acid (MLFA) and PNFA. According to CP-MAS 13C NMR experiments the carbohydrate content in Vestfold Hills fulvic acid is higher than that of Pony Lake Fulvic Acid (PLFA), suggesting that dissolved organic matter (DOM) from Vestfold Hills Lakes is immature. TMAH–GC-MS demonstrated that Antarctic fulvic acids are enriched in heterocyclic non-aromatic nitrogen-containing components such as pyrimidine structures, with the exception of OLFA. Furthermore, tricyclic terpenoids (dehydroabietic acid) were detected in two out of four fulvic acids tabulated using TMAH–GC-MS. Although diterpenes are commonly associated with plants and fungi, their occurrence in Antarctic fulvic acids could be justified due to their diverse origins from cyanobacteria to aerosols.