Tracking POPs across the planet | News Briefs: Guidelines for purifying water ` Is your city sustainable? ` Green computers ` Biofuels poised to displace oil ` Ozone healing delayed ` A wiki of a different kind | Efforts to stop groundwater pollution disappoint | Pinpointing where plants store arsenic | Coal utilities gamble on carbon regulation | Canada eyes limits on nonstick chemicals | Janet G. Hering to direct Swiss Eawag | Keeping up with the Johnsons