Metaldehyde is dangerous to cats, dogs, birds and other wildlife if ingested. It is also dangerous to aquatic life as it leaches from the from degraded pellets into the soil and can be dissolved in run-off during heavy rain events into water courses.
Two useful web articles on Metaldehyde are:
GAFA voted as a group in January 2011 to prohibit the use of metaldehyde-based slug pellets at St Mary’s Rd allotments – because other equally effective treatments exist that are either safe to most wildlife or pose only a very low risk of illness.
The effective alternatives to metaldehyde are:
1) “Organically approved” slug pellets based on Ferric Phosphate – which do not pose a risk of death or serious illness to pets or wild animals when applied as instructed on the bottle (you don’t need larger amounts – I’ve used these for 4 years and if they work well if applied every 2 weeks). Ferric phosphate is a sparingly soluble salt and is a natural constituent of most types of soil. These pellets are available from Glossop Garden Centre and most other outlets. They are effective, when eaten by slugs/snails and particularly protect against those moving across the soil surface from other parts of the garden. Something we see a lot of in Glossopdale.
2) Beer bait traps (with rain covers).
3) Nematode treatment applied from a watering can – protects against slug damage underground – but is less effective on the surface (Available online or from garden centres)
4) Wool barriers around the base of valuable plants.
5) Copper tape stuck to the rim of large pots – serrated tape will also act as a barrier to snails (available online or from garden centres).