Changes in pesticide occurrence in suburban surface waters in Massachusetts, USA, 1999-2010.

Pesticide occurrence was determined in two suburban surface waters in eastern Massachusetts, USA during 2009 and 2010. Out of 118 collected samples, 45 samples showed detections of one or more target pesticides. Among the herbicides, 2,4-D was the most frequently detected and imidacloprid was the most frequently detected insecticide.

Formation of pi-pi complexes between phenanthrene and model pi-acceptor humic subunits.

Pi-pi interactions may play a role in association of aromatic compounds with natural organic substances. Complexation in aqueous solvents was studied between the pi donor, phenanthrene (PHEN), and model pi-acceptor species (quinones and N-heteroaromatic cations) that represent certain functional units of humic substances. Charge-transfer bands in the UV and ring-current shifts in the proton nuclear magnetic resonance (NMR) spectrum confirmed the face-to-face, pi-pi donor-acceptor nature of the bond.