Bee-threatening soil residue up to 14x ‘safe’ levels - study

Evidence suggests the concentrations of neonicotinoid soil residues identified in the new study are potentially harmful to bees and other beneficial insects, but non-toxic to humans.

Dr Chris Pook, now at the University of Auckland-based Liggins Institute, and Dr Iana Gritcan from AUT sampled soil for residues of neonicotinoid insecticides from maize fields in the Bay of Plenty, East Coast and the floodplains of the Waikato, regions known for long-term maize growing. These sites were selected after local beekeepers reported, over several years, unexplained losses of hives wintered in these areas.

Neonicotinoids are most commonly applied as a coating on planted seeds, which dissolves and disperses into the soil, and recent research shows traces can remain for months or years.

Tests revealed that, in 43 out of 45 samples, concentrations of neonicotinoid residues exceeded the Environmental Exposure Limit set by the New Zealand Environmental Protection Agency (NZEPA), which is one nanogram of imidacloprid per gram of dry soil (about one part per billion). The average concentration of imidacloprid across all sites was 5.1 parts per billion; the highest measured was 13.7 parts per billion.

Imidacloprid is one of three neonicotinoids licenced for use in Aotearoa New Zealand as seed coatings. NZEPA have not set residue limits for the other two, thiamethoxam, clothianidin. However, the researchers also found residues from clothianidin across all 45 sites (average 8.2 parts per billion, and up to 109.3 parts per billion).

“Either the NZEPA has overestimated the hazard from neonicotinoids, and these levels are nothing to worry about, or it’s got its threshold right and these findings flag up a huge problem,” says Dr Pook, a research fellow at the Liggins Institute.

“There’s robust evidence that these kinds of concentrations are accessible to pollinators via a multitude of routes – via flowering plants, or residues leeched into surface water, for example.”

In Europe, the use of neonicotinoid insecticides was heavily restricted after the European Food Safety Agency accepted concerns raised by scientists and conservationists about their detrimental consequences for non-target species.

In New Zealand, there are no such restrictions, and nor is there any requirement to keep sales records, so it is not possible to tell whether neonicotinoid use is rising or falling. Anecdotal evidence suggests it’s used widely across the country and for a variety of crops, especially for maize.

Dr Pook pointed to the recent comments from the Parliamentary Commissioner for the Environment, Simon Upton, who highlighted that the way NZ collects and uses data about the environment could be leading to poor policy decisions and environmental damage. “It’s a classic example of how you can’t manage what you don’t measure,” says Dr Pook.

“Even if New Zealand’s use of neonicotinoids is not increasing, the annual application of neonicotinoids, whose residues persist for more than a year, may cause their accumulation in the soil of the country’s fields,” he says.

The consequences for New Zealand’s biodiversity are unclear. The study authors point to evidence from the Netherlands that the abundance and diversity of both freshwater invertebrates and insectivorous birds are heavily reduced in areas where neonicotinoid concentrations in surface waters exceed about one hundred nanograms per litre, or one hundred parts per trillion.

But, there is no way of telling if this is an issue in New Zealand because we appear to have no reported measurements of neonicotinoid in surface water.

“Our study was not designed to assess the impact of neonicotinoid residues upon bees and we are not suggesting a link between the soil residues and the reported beehive losses,” says Dr Pook. “However, in light of our findings, the effects of these residues upon non-target insects in New Zealand’s agricultural communities should be investigated and the risks associated with their continued use reviewed by the NZEPA.”

The study is published in Environmental Pollution.