Moorland grouse - Flubendazole use for parasitic worm control: preliminary environmental assessment

6. Conclusions and recommendations

Information on environmental exposure of flubendazole for its use in medicated grit on moorlands for the treatment of worm in grouse is lacking. The most relevant pathways to the environment are via the faeces of treated birds and leaching from spilt or open piles of medicated grit, if best practice is not followed. Based on these pathways of release and the substance’s properties, the target environmental compartments are soil and surface waters (the latter likely to be from both dissolved fraction and sorbed particulate run off).

Estimates of environmental exposure on and near moorlands are uncertain. However, based on some conservative assumptions levels in soil are likely to be low. Concentrations dissolved in surface waters are also likely to be low, but it has not been possible to model concentrations associated with particulate runoff. This is likely to be a more significant transport pathway than the dissolved fraction given flubendazole’s properties.

Once in water, flubendazole is likely to partition to sediment. Sediment exposure has been estimated based on the dissolved fraction entering watercourses only. This means water and sediment concentrations may be underestimated especially in the case of malpractice (i.e. spilt or open piles of medicated grit placed too near watercourses). This is a datagap in the exposure assessment that would require further work.

As the daily dose in the grouse is low, the substance has a low potential for bioaccumulation and the majority of the administered dose that is absorbed is metabolised. Exposure in animals that may predate or scavenge on grouse carcasses is therefore likely to be low.

Ecotoxicity data for flubendazole are limited to marine bacteria, aquatic plants and invertebrates. Invertebrates are more sensitive to the substance than the other tested species. These data have been used to estimate equivalent levels of toxicity for soil- and sediment-dwelling organisms. Estimates, however, are uncertain and can only be used to form indicative conclusions on hazard for these environmental compartments. Taking account of these uncertainties predicted thresholds of effect are orders of magnitude above compartment specific predicted concentrations as modelled in this report.

Although the assessment in this report has generally presented a low environmental risk from the use of flubendazole in medicated grit on grouse moors, the uncertainties in both the estimated environmental concentrations and ecotoxicological effects data are high enough for us to recommend:

• An investigation into levels of flubendazole in surface waters (and sediments) and potentially impacted invertebrate communities near or on moorlands using medicated grit be considered to confirm that best practice is protective of the local environment. Sampling for chemical analysis should be conducted to reflect both dry and wet periods and be carried out during the main periods of use (winter – early summer)
• If there is a need to investigate instances of grit malpractice, “walk overs” or other visual inspection methods (eg unmanned aerial reconnaissance) should be considered since ecological and chemical monitoring are unlikely to give much information on this.
• Refining this report should new information on ecotoxicity or modelling approaches relevant for particulate run off become available to improve predictions of levels in water and sediments and their potential impact on wildlife.