Widespread Microbial Adaptation to l-Glutamate-N,N-diacetate (L-GLDA) Following Its Market Introduction in a Consumer Cleaning Product

Abstract

l-Glutamate-N,N-diacetate (L-GLDA) was recently introduced in the United States (U.S.) market as a phosphate replacement in automatic dishwashing detergents (ADW). Prior to introduction, L-GLDA exhibited poor biodegradation in OECD 301B Ready Biodegradation Tests inoculated with sludge from U.S. wastewater treatment plants (WWTPs). However, OECD 303A Activated Sludge WWTP Simulation studies showed that with a lag period to allow for growth (40-50 days) and a solids retention time (SRT) that allows establishment of L-GLDA degraders (>15 days), significant biodegradation (>80% dissolved organic carbon removal) would occur. Corresponding to the ADW market launch, a study was undertaken to monitor changes in the ready biodegradability of L-GLDA using activated sludge samples from various U.S. WWTPs. Initially all sludge inocula showed limited biodegradation ability, but as market introduction progressed, both the rate and extent of degradation increased significantly. Within 22 months, L-GLDA was ready biodegradable using inocula from 12 WWTPs. In an OECD 303A study repeated 18 months post launch, significant and sustained carbon removal (>94%) was observed after a 29-day acclimation period. This study systematically documented field adaptation of a new consumer product chemical across a large geographic region and confirmed the ability of laboratory simulation studies to predict field adaptation.

Implications of microbial adaptation for the assessment of environmental persistence of chemicals

“…In respect to biodegradation, adaptation can be defined as an evolutionary process in which a change in the microbial community or organisms takes place and which is manifested by an increase in the biodegradation rate of a chemical (Itrich et al, 2015;Kowalczyk et al, 2015;Wiggins, Jones, & Alexander, 1987). Of course, in other fields microbial adaptation may be defined differently, such as in the field of eukaryotic host-microorganism interactions (Ochman & Moran, 2001;van der Meer & Sentchilo, 2003).…”

“…One of the major reported factors causing variability in the RBTs is the source of the inoculum (Dick et al, 2016;Martin et al, 2017;Mezzanotte, Bertani, Innocenti, & Tosin, 2005;Thouand, Capdeville, & Block, 1996;Thouand et al, 2011;V azquez-Rodr ıguez, Garab etian, & Rols, 2007). The quality of the inoculum is affected by i) the total cell density (Blok & Booy, 1984;Martin et al, 2017;Thouand et al, 1995;V azquez-Rodr ıguez et al, 2007), ii) the diversity of the community (Forney et al, 2001), iii) the ratio between nutrients and biomass (F/M ratio) (Vazquez-Rodriguez, Palluy, Goma, & Rols, 1999), and iv) the origin and exposure history (Itrich et al, 2015;Kim et al, 2017;Mezzanotte et al, 2005;Thouand et al, 1996).…”

“…The origin and history of an inoculum determines its composition and diversity as the result of a long evolutionary process of successive microbial adaptations (Itrich et al, 2015;Kowalczyk et al, 2015). Microorganisms are able to develop mechanisms of resistance and metabolism once exposed to novel environmental pollutants (van der Meer, 2006).…”

“…As a result, members of the community can increasingly withstand the potential toxic effects of chemicals or even degrade them (Lo Giudice et al, 2013;Saez, Aparicio, Amoroso, & Benimeli, 2015;Zhuang, Tay, Yi, & Tay, 2005). Therefore, microbial adaptation and microbial evolution can be crucially important when assessing the biodegradation of chemicals (Comber & Holt, 2010;Itrich et al, 2015;Markiewicz et al, 2011). More importantly, it explains why the variability in different biodegradability tests yields a low predictive value for the environmental persistency of chemicals (Thouand et al, 2011).…”

“…More importantly, it explains why the variability in different biodegradability tests yields a low predictive value for the environmental persistency of chemicals (Thouand et al, 2011). It also becomes evident why results of RBTs change over time as microbial populations apparently adapt within years or even months to metabolize chemicals which were previously considered to be persistent (Itrich et al, 2015). Finaly, it could also explain the hight percentage of chemicals, not yet released in the environment, that tend to fail the test, as the inoculum has not been exposed to the chemical yet (Painter, 2002).…”