Interlaboratory Validation of Toxicity Testing Using the Duckweed Lemna minor Root-Regrowth Test.

The common duckweed (Lemna minor), a freshwater monocot that floats on the surfaces of slow-moving streams and ponds, is commonly used in toxicity testing. The novel Lemna root- regrowth test is a toxicity test performed in replicate test vessels (24-well plates), each containing 3 mL test solution and a 2-3 frond colony. Prior to exposure, roots are excised from the plant, and newly developed roots are measured after 3 days of regrowth. Compared to the three internationally standardized methods, this bioassay is faster (72 h), simpler, more convenient (requiring only a 3-mL) and cheaper. The sensitivity of root regrowth to 3,5-dichlorophenol was statistically the same as using the conventional ISO test method. The results of interlaboratory comparison tests conducted by 10 international institutes showed 21.3% repeatability and 27.2% reproducibility for CuSO4 and 21.28% repeatability and 18.6% reproducibility for wastewater. These validity criteria are well within the generally accepted levels of <30% to 40%, confirming that this test method is acceptable as a standardized biological test and can be used as a regulatory tool. The Lemna root regrowth test complements the lengthier conventional protocols and is suitable for rapid screening of wastewater and priority substances spikes in natural waters.

Preparation and Application of Light-Colored Lignin Nanoparticles for Broad-Spectrum Sunscreens.

Recently, natural sun blockers have been drawing considerable attention because synthetic UV filters could have adverse effects not only on humans but also on the environment. Even though lignin, the second most abundant renewable resource on earth, is a natural UV-absorbing polymer, its unfavorable dark color hampers its applications in sunscreens. In this work, we obtained light-colored lignin (CEL) from rice husks through cellulolytic enzyme treatment and subsequent solvent extraction under mild conditions and compared CEL to technical lignin from rice husks using the International Commission on Illumination L*a*b* (CIELAB) color space. Spherical nanoparticles of CEL (CEL-NP) were also prepared using a solvent shifting method and evaluated for broad-spectrum sunscreens. A moisturizing cream blended with CEL-NP exhibited higher sun protection factor (SPF) and UVA PF (protection factor) values than that with CEL. In addition, CEL-NP had synergistic effects when blended with an organic UV-filter sunscreen: CEL-NP enhanced the SPF and UVA PF values of the sunscreen greatly. However, there was no synergistic effect between CEL-NP and inorganic sunscreens. We expect nanoparticles of light-colored lignin to find high-value-added applications as a natural UV-blocking additive in sunscreens and cosmetics.

Adsorptive removal of tetracycline from aqueous solution by maple leaf-derived biochar.

The present study evaluates the physicochemical properties of maple leaf-derived biochars (M-BCs) produced at different pyrolytic temperatures (i.e., 350, 550, and 750 °C) and their adsorptive properties for tetracycline onto M-BCs. The increase in pyrolysis temperature to produce M-BCs led to a significant increase in the biochar's hydrophobicity, surface area, and calcite (CaCO3) crystallization. The M-BC750 produced without functionalization or activation possessed a high calcite composition and a hydrophobic nature with lower O/C and H/C, hydroxyl groups (-OH) on the surface, and functional groups (i.e., O-containing) as H-bond acceptors. Among M-BCs, the M-BC750 present a highest TC adsorption capacity owing to possible mechanisms such as metal complexation, H-bonding, and hydrophobic interactions. The isotherm and kinetic models for TC adsorption followed the Freundlich models and pseudo-second-order models, respectively. M-BCs produced from the waste fallen maple leaves could be applied as low-cost environmental adsorbents for TC removal.

Tracing lead pollution sources in abandoned mine areas using stable Pb isotope ratios.

This study focused on Pb isotope ratios of sediments in areas around an abandoned mine to determine if the ratios can be used as a source tracer. For pretreatment, sediment samples were dissolved with mixed acids, and a multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS, Nu plasma II) was used to investigate the Pb isotopic composition of the samples. The measured isotope ratios were then corrected for instrumental mass fractionation by measuring the (203)Tl/(205)Tl ratio. Repeated measurements with the NIST SRM 981 reference material showed that the precision of all ratios was below 104 ppm (±2σ) for 50 ng/g. The isotope ratios ((207)Pb/(206)Pb) found were 0.85073 ± 0.0004~0.85373 ± 0.0003 for the main stream, while they were 0.83736 ± 0.0010 for the tributary and 0.84393 ± 0.0002 for the confluence. A binary mixing equation for isotope ratios showed that the contributions of mine lead to neighboring areas were up to 60%. Therefore, Pb isotope ratios can be a good source tracer for areas around abandoned mines.