WRAP Research: Persistent herbicides in digestate

The detection of herbicides in composting and AD is the subject of new research published by WRAP. Two separate reports “Detecting persistent herbicides in anaerobic digestion” and “Detecting persistent herbicides in compost” explore the impact of herbicides in digestate and compost respectively.

Detecting persistent herbicides in anaerobic digestion

This investigation looked into what happens to persistent herbicides in wet, mesophilic anaerobic digestion systems. The experience showed that standard analytical techniques are unsuitable to detect a majority of herbicides used in this experiment. During the experiment, it was found that herbicides could be extracted in aqueous samples but not digestate samples, suggesting a flaw in the extraction technique. The rest of the experiment was then focused on developing a method to recover more herbicides.

WRAP state that previous risk assessment work suggests that the risk of herbicide residues in crops and manures being transferred via AD to sensitive crops is none-to-low.  Nonetheless, the research highlights the importance of agricultural herbicide users following product instructions for disposing of treated plant residues and manures.

For more information about the experiment, read the final report here.

Detecting persistent herbicides in compost

This investigation looked into the levels of compost contamination from grass clippings entering the green waste stream, which may contain residues of persistent herbicides and how many of these survive the composting process.

WRAP state that they found that herbicide contamination will not cause any problems in the majority of applications and certainly not in agriculture.  Although it is quite common to find herbicide residues in composts, using the field bean plant response test provides a robust mechanism for preventing them from becoming a problem even in the most sensitive scenarios.  WRAP recommends that compost destined for use in growing media is tested using the field bean test, published by the Compost Certification Scheme

For more information about the experiment, read the final report here.