Environmental fate and microbial degradation of aminopolycarboxylic acids

Abstract

Aminopolycarboxylic acids (APCAs) have the ability to form stable, water-soluble complexes with di- and trivalent metal ions. For that reason, synthetic APCAs are used in a broad range of domestic products and industrial applications to control solubility and precipitation of metal ions. Because most of these applications are water-based, APCAs are disposed of in wastewater and reach thus sewage treatment plants and the environment, where they undergo abiotic and/or biotic degradation processes. Recently, also natural APCAs have been described which are produced by plants or micro-organisms and are involved in the metal uptake by these organisms. For the two most widely used APCAs, nitrilotriacetate (NTA) and ethylenediaminetetraacetate (EDTA), transformation and mineralisation processes have been studied rather well, while for other xenobiotic APCAs and for the naturally occurring APCAs little is known on their fate in the environment. Whereas NTA is mainly degraded by bacteria under both oxic and anoxic conditions, biodegradation is apparently of minor importance for the environmental fate of EDTA. Photodegradation of iron(III)-complexed EDTA is supposed to be mostly responsible for its elimination. Isolation of a number of NTA- and EDTA-utilising bacterial strains has been reported and the spectrum of APCAs utilised by the different isolates indicates that some of them are able to utilise a range of different APCAs whereas others seem to be restricted to one compound. The two best characterised obligately aerobic NTA-utilising genera (Chelatobacter and Chelatococcus) are members of the alpha-subgroup of Proteobacteria. There is good evidence that they are present in fairly high numbers in surface waters, soils and sewage treatment plants. The key enzymes involved in NTA degradation in Chelatobacter and Chelatococcus have been isolated and characterised. The two first catabolic steps are catalysed by a monooxygenase (NTA MO) and a membrane-bound iminodiacetate dehydrogenase. NTA MO has been cloned and sequenced and its regulation as a function of growth conditions has been studied. Under denitrifying conditions, NTA catabolism is catalysed by a NTA dehydrogenase. EDTA breakdown was found to be initiated by a MO also which shares many characteristics with NTA MO from strictly aerobic NTA-degrading bacteria. In contrast, degradation of [S,S]-ethylenediaminedisuccinate ([S,S]-EDDS), a structural isomer of EDTA, was shown to be catalysed by an EDDS lyase in both an EDTA degrader and in a NTA-utilising Chelatococcus strain. So far, transport of APCAs into cells has only been studied for EDTA and the results obtained give strong evidence for an energy-dependent carrier system and Ca(2+) seems to be co-transported with EDTA. Due to their metal-complexing capacities, APCAs occur in the environment mostly in the metal-complexed form. Hence, the influence of metal speciation on various degradation processes is of utmost importance to understand the environmental behaviour of these compounds. In case of biodegradation, th...

Enhanced phytoextraction of Cu, Pb, Zn and Cd with EDTA and EDDS

“…Although EDTA is very effective in mobilizing metals in soils, EDTA and EDTA-heavy metal complexes can be toxic to plants and soil microorganisms and they can be also persistent in the environment due to their low biodegradability (Bucheli-Witschel and Egli, 2001;Grčman et al, 2003).…”

Speciation of metal–EDTA complexes by flow injection analysis with electrospray ionization mass spectrometry and ion chromatography with inductively coupled plasma mass spectrometry

“…Chelating agents occur in natural waters predominantly as metal complexes. There are many studies emphasizing the importance of chelation on metal bioavailability, plant uptake, toxicity, transport, adsorption, distribution, and fate [3]. However, the identification and detection of these metal complexes in environmental sample is still a significant analytical challenge because of their structural similarities and presence at low concentrations in environmental matrices [4].…”

Influence of [S, S]-EDDS on Phytoextraction of Copper and Zinc byElsholtzia SplendensFrom Metal-Contaminated Soil

“…However, potential side effects related to the addition of chelants, such as metal leaching to groundwater, have led to health, safety, and environmental concerns. Many synthetic chelants and their complexes with heavy metals can have negative effects on the environment (Bucheli-Witschel and Egli, 2001) and are poorly photo-, chemo-, and biodegradable in soils (Bucheli-Witschel and Egli, 2001;Egli, 2001;Kari and Giger, 1996;Nortemann, 1999). EDDS, a structural isomer of EDTA, is a promising new alternative synthetic chelant.…”