Forecasting leachate generation from pilot woodchip stockpiles using a three-dimensional transient flow model.

Leachate generation from open stockpiles of recycled woodchip materials is potentially harmful to aquatic ecosystems. There is growing interest in using numerical models to simulate leachate generation from outdoor piles, but this requires information about the hydraulic properties of the materials. The objectives of this study were to simulate leachate from woodchip piles with the numerical model HYDRUS-3D and to optimize subsets of parameters for single (SPM) and dual (DPM) pore flow models with the Bayesian Markov Chain Monte Carlo algorithm DREAMZS. Three experimental piles, each approximately 30 m3, were setup with mixtures of either once (coarse) or twice (fine) ground woodchips. Leachate continuously collected over a period of six months was similar across piles. As a result, subsets of optimized flow parameters for the coarse and fine woodchips were not different. Leachate predictions by the two pore flow models were similar and agreed reasonably with the field measurements, as indicated by Nash-Sutcliffe efficiency values greater than 0.6. This result suggests the simpler SPM is adequate for field predictions of leachate. However, leachate was consistently under-predicted by both pore models by 13-27% during rainfall events with more than 1 cm in 6 h. The optimized flow models can be used as a tool for studying pile management strategies.

Freshwater Crayfish: A Potential Benthic-Zone Indicator of Nanosilver and Ionic Silver Pollution.

Nowadays, silver nanoparticles (AgNPs) are utilized in numerous applications, raising justified concerns about their release into the environment. This study demonstrates the potential to use freshwater crayfish as a benthic-zone indicator of nanosilver and ionic silver pollution. Crayfish were acclimated to 20 L aquaria filled with Hudson River water (HRW) and exposed for 14 days to widely used Creighton AgNPs and Ag(+) at doses of up to 360 µg L(-1) to surpass regulated water concentrations. The uptake and distribution of Ag in over 650 exoskeletons, gills, hepatopancreas and muscles samples were determined by inductively coupled plasma optical emission spectroscopy (ICP-OES) in conjunction with two complementary U.S. EPA-endorsed methods: the external calibration and the standard additions. Reflecting the environmental plasticity of the two investigated species, Orconectes virilis accumulated in a dose-dependent manner more Ag than Procambarus clarkii (on average 31% more Ag). Both species showed DNA damage and severe histological changes in the presence of Ag. However, Ag(+) generally led to higher Ag accumulations (28%) and was more toxic. By the harvest day, about 14 ± 9% of the 360 µg L(-1) of AgNP exposure in the HRW oxidized to Ag(+) and may have contributed to the observed toxicities and bioaccumulations. The hepatopancreas (1.5-17.4 µg of Ag g(-1) of tissue) was identified as the best tissue-indicator of AgNP pollution, while the gills (4.5-22.0 µg g(-1)) and hepatopancreas (2.5-16.7 µg g(-1)) complementarily monitored the presence of Ag(+).