Comparison of Microtox and Xenoassay Light as a Near Real Time River Monitoring Assay for Heavy Metals

Abstract

Luminescence-based assays for toxicants such as Microtox, ToxAlert, and Biotox have been used extensively worldwide. However, the use of these assays in near real time conditions is limited due to nonoptimal assay temperature for the tropical climate. An isolate that exhibits a high luminescence activity in a broad range of temperatures was successfully isolated from the mackerel, Rastrelliger kanagurta. This isolate was tentatively identified as Photobacterium sp. strain MIE, based on partial 16S rDNA molecular phylogeny. Optimum conditions that support high bioluminescence activity occurred between 24 and 30°C, with pH 5.5 to 7.5, 10 to 20 g/L of sodium chloride, 30 to 50 g/L of tryptone, and 4 g/L of glycerol as the carbon source. Assessment of near real time capability of this bacterial system, Xenoassay light to monitor heavy metals from a contaminated river running through the Juru River Basin shows near real time capability with assaying time of less than 30 minutes per samples. Samples returned to the lab were tested with a standard Microtox assay using Vibrio fishceri. Similar results were obtained to Xenoassay light that show temporal variation of copper concentration. Thus, this strain is suitable for near real time river monitoring of toxicants especially in the tropics.

Improvement of Ficin-Based Inhibitive Enzyme Assay for Mercury Using Response Surface Methodology and Its Application for Near Real-Time Monitoring of Mercury in Marine Waters

“…There is negligible Preprints (www.preprints.org) | NOT PEER-REVIEWED | Posted: 31 August 2020 doi:10.20944/preprints202008.0689.v1 inhibition (<10%) to the ficin assays and instrumental analysis shows mercury level lower than the designated MPL in marine waters (0.040 mg/L). Other near real-time works using enzymes in rivers shows temporal levels of heavy metals [9,11,13,14,35] and this is the first study using marine water as samples. Marine waters are large bodies of water where heavy metals originating from terrestrial areas are rapidly diluted.…”

“…Ficin activity and optimization studies based on OFAT were carried out according to previous work [14]. To match ambient temperature for field trial environment in Malaysia and to qualify for near-real-time measurement, the temperature was fixed at 30 C and the incubation duration was fixed for 30 min [10,11,18].…”

“…This could explain the lack of inhibition to the ficin and a lower concentration of mercury in marine waters within this area. Variation in heavy metals levels in running water especially in rivers and marine water bodies is common [9][10][11][12][13]37]. Even sedimentary samples have been found to be variable in their spatial and temporal concentrations of heavy metals [38].…”

“…In enzyme assays, the sampling to detection period can be carried out in less than one hour using a portable spectrophotometer and thus is a perfect candidate for near real-time analysis. We have demonstrated the application of enzyme-based system in capturing in near real-time the temporal variation of heavy metals concentrations in rivers running through heavily industrialized areas [9][10][11][12][13]. The application of the ficin assay in monitoring mercury in marine water bodies in this study is a novel exercise meant as a proof of concept.…”

“…Being able to monitor bioavailable mercury in near real-time (less than 1 h detecting time) allows the temporal detection of heavy metals that often elude monitoring authorities [3][4][5]. Previously, we have developed several heavy metal inhibition assays based on proteases including papain [6], bromelain [7], trypsin [8] which show promising potential in near real-time monitoring of heavy metals [9][10][11][12][13]. Previously, we had developed an inhibitive assay using ficin [14], which has the most sensitive response to mercury with an IC50 value of 0.085 mg/L.…”