Lemon juice, both from freshly squeezed lemons and packaged lemon juice sold for cooking, contains citric acid and is sometimes used to dissolve brown heroin for injection.
There is research showing that lemon juice can carry fungal infections, which can infect the heart (endocarditis) and eyes (candidal endopthalmitis). The candidal fungi lives on the skins of the lemons when they are growing on the tree, when the lemons are processed the fungus is transferred to the juice.
Among needle exchange workers attending our safer injecting courses during 2000/1, there was a rapid increase in awful stories of eyesight loss due to candidal endopthalmitis amongst their clients.
This was almost caused by the difficulties drug users were experiencing in buying citric acid, and the resulting increase in the use of lemon juice and vinegar as acidifiers, and was a significant part of the reason we were so motivated to source and supply sachets.
Candidal fungal contamination of vinigar is also possible.