Elisa M. D’Angelo

Tetracycline desorption kinetics in municipal biosolids and poultry litter amendments determined by diffusive gradients in thin films (DGT)

Tetracycline (TET) is commonly used to treat bacterial diseases in humans and chickens (Gallus gallus domesticus), is largely excreted, and is often found at elevated concentrations in treated sewage sludge (biosolids) and poultry litter (excrement plus bedding materials). Land spreading of these materials is practiced worldwide to improve soil fertility, but the practice raises questions about whether TET could be released to the environment and cause adverse effects. Hazard risks largely depend on the concentration in the solid phase that can be released to the solution phase (labile TET), its desorption rate constant, and diffusion rate of dissolved TET in amendments. In this study, these quantities were evaluated in biosolids and three types of litter amendments by combinations of equilibrium sorption-desorption isotherm and desorption kinetic studies using diffusive gradient in thin films (DGT) samplers. Results from isotherm experiments showed that TET partitioning was inhibited at the high dissolved organic carbon (DOC) concentrations in amendments (6-15% of dry mass). Despite low partition coefficients determined at high particle/DOC concentrations of amendments (Kd = 9-46 mL g-1), results from DGT experiments revealed that TET release by desorption and diffusion would be slow and short-lived (<3 d) due to small effective diffusion coefficients (<8 × 10-8 cm2 s-1) and low concentrations of labile TET in amendments (<5% of total TET). Despite this, evaluations of antibiotic uptake during microbial colonization and plant root interception of amendment surfaces are highly warranted.

Detection of polychlorinated biphenyls employing chemical dechlorination followed by biphenyl whole cell sensing system

Polychlorinated biphenyls (PCBs) are a mixture of 209 individual chlorinated compounds commonly known as PCB congeners. These compounds are hydrophobic and are persistent in the environment. Their use was banned in the US a few decades ago because of harmful health effects. Therefore, detection of PCBs in environmental samples is increasingly important. To that end, we have developed a two-step simple and sensitive method for the detection of total PCBs. Specifically, our method involves dechlorination of PCBs to biphenyl followed by detection of biphenyl using a whole cell sensing system as the detection system. The whole cell sensing system consists of cells of the strain Pseudomonas pseudoalcaligenes KF707 harboring plasmid pSD7000. Plasmid pSD7000 contains the gene of lacZ, a reporter protein under the control of the bph operon. The detection is achieved through the emission of light afforded by the expression of reporter protein triggered by the presence of biphenyl. Due to the fact that this operon is activated only by few PCB congeners, a chemical dechlorination method was employed to convert all PCBs to biphenyl, and thus all the PCBs present in a given sample are able to be detected. The results showed that PCB congeners were rapidly (30 min) and efficiently (>98.5%) dechlorinated to biphenyl using a Mg/K2PdCl6 catalyst, and the biphenyl could be subsequently quantified using the whole cell sensing system. This hybrid analytical method that combines classical dechlorination with novel biosensing methods may find applications in the on-site monitoring of PCBs contamination levels.