Dissipation of polycyclic aromatic hydrocarbons in crop soils amended with oily sludge

Oil fields present a potential ecological risk to nearby farmland soil. Here we present a new method designed to evaluate the ability of winter wheat(Triticum aestivum) to contribute to the dissipation of polycyclic aromatic hydrocarbons(PAHs), which are priority pollutants in soils contaminated by oily sludge. The influence of different doses of oily sludge on the dissipation of PAHs was studied along with individual PAH profiles in soils after different periods of plant growth. Five soil samples were artificially contaminated with different percentages of oily sludge(0 %, 5 %, 10 %, 15 % and 20 %). Winter wheat grew in the oily sludge–amended soils for 265 days.PAH content in the soils was monitored over the course of the study. The rate of PAH dissipation is related to the properties of different PAHs, period of winter wheat growth, and oily sludge application dose. Analysis for treated soils indicates that the dissipation of PAHs increased significantly over the first 212 days, followed by minimal changes over the final 53 days of treatment. In contrast, PAH dissipation slowed with increasing oily sludge application. For each PAH, the experimental results showed a significant compound-dependent trend. Winter wheat in the present study significantly enhanced the dissipation of PAHs in oily sludge–contaminated soil.

Accelerated biogenic silica dissolution by marine invertebrate digestion:in comparison with phosphorus and iron

Herbivore digestion in aquatic ecosystems is usually considered a method of nutrient repackaging rather than recycling,as recalcitrant and low-level nutrients are presumed for their egesta.We hypothesize that this opinion holds only for nutrients recycled by excretion and egestion,not for those elements recycled overwhelmingly by fecal decomposition.In this study,we compared the dissolution of biogenic silica(BSi),phosphorus(P)and iron(Fe)between two food items and fecal pellets of two marine invertebrates fed on artificial seawaters free of bacteria.Relative to raw food materials,the mass proportion in fecal pellets of BSi increased,while that of P and Fe decreased.During the 21 days of incubation,the total dissolution rate of BSi was 13.9–36.0 times higher in fecal pellets than food items,followed by P(1.5–4.2 times)and Fe(1.1–2.4 times).While the dissolution of BSi and Fe occurred mostly in the first few days,P was mostly released in the last ten days.Regarding BSi dissolution,a higher rate was observed in oyster Crassostrea gigas than the Echiuran Urechis unicinctus,but no significant difference was found between fecal pellets in either species under naturally available diatom food(Phaeodactylum tricornutum)and introduced terrestrial food(rice husk powder),respectively.Our results show direct evidence of digestion-associated nutrients mobilization.BSi dissolution after animal digestion may be similarly efficient to that caused by bacteria colonization in natural seawater.