Needles discarded in open spaces by injection drug users (IDUs) represent an important sign of social disorder that degrades community quality-of-life and provokes intolerance of much-needed health services, such as needle exchange programs (NEP). Discarded needles (discards) also represent a rare means of studying the environmental behavior of IDUs, as typically a needle is discarded at or near the site of injection.

Here harm reduction and risk environment theory provide a framework for two distinct analyses of an exceptional set of discard data, which includes the geocoded locations of over 7,000 needles collected monthly over a five-year period for a 2.5km² (one square-mile) area encompassing the most active drug-use neighborhood in Montréal, Canada.

The first analysis was an assessment of a safe disposal program. It used Quasi-Poisson regression to compare discard rates before and after the installation of needle drop-boxes, adjusting for known time-dependent covariates. Drop-boxes were associated with large reductions in discards; the association was inversely proportional to distance: reductions ranged from 59% [95% CI: 30-76%] for areas within a 200m (656ft) walking distance around drop-boxes to 96% [95% CI: 91-98%] for 25m (82ft) walking areas.

The second analysis, which required innovative GIS-based environmental measurement techniques, was more exploratory in nature. It followed a spatial case—control approach to test a conceptual model of the ecology of discarding, operationalized through 35 measures of the physical and social environment, of which 18 were significant. The strongest apparent attractor of discards was proximity to a single point-of-sale; the strongest apparent deterrent was visual exposure. Measures of drug and drug-funding acquisition were most frequently associated with discards. Measures of social control were surprisingly poor predictors of discards.

The dissertation's findings provide evidence that (a) IDUs are socially conscious, if highly constrained, individuals who will make significant efforts to reduce their harm to others when provided with the means to do so; and (b) their spatial behavior is adaptive, partially predictable, and influenced measurably by environmental settings. Taken as a whole, these findings suggest that physical interventions—whether service provision or urban design—are promising tools for reducing discards and managing public injection.