The relative toxicity of metaldehyde and iron phosphate-based molluscicides to earthworms

Slugs are suppressed by cereal flour-based baits or pellets containing metaldehyde, or containing iron phosphate plus chelating agents, which are also consumed by earthworms and other invertebrates. These studies compared the effects of metaldehyde and iron phosphate alone, with those of iron phosphate plus chelating agents EDDS and EDTA, and of the chelating agents alone on earthworms.OECD artificial soil testEarthworms (Eisenia fetida) were exposed directly to the molluscicides in artificial soil. The test chemicals were: metaldehyde; iron phosphate; ethyldiaminetetraceticacid (EDTA), ethylenediaminesuccinicacid (EDDS) and mixtures of iron phosphate and these latter two chemicals. LD50 values were more than 10,000 mg kg−1 for metaldehyde and iron phosphate, 156.5 mg kg−1 for EDTA, 145.6 mg kg−1 for EDDS, 72.2 mg kg−1 for iron phosphate/EDTA, and 83.0 mg kg−1 for iron phosphate/EDDS.Microcosm testFour mature Lumbricus terrestris were exposed in each microcosm (15 cm diam. × 30 cm deep) to pellets containing: no active ingredient; metaldehyde (4%); iron phosphate/EDTA (1%) (Sluggo®); iron phosphate (3%); EDTA (3%); EDDS (3%). Metaldehyde and iron phosphate did not affect earthworm feeding, growth or mortality. Sluggo® decreased earthworm feeding and caused loss of weight and mortality. Earthworms consumed fewer pellets containing EDDS or EDTA and lost weight.