Are pesticide residues in honey related to oilseed rape treatments?

Highlights

• The amount of pesticide residues in honey can vary largely between the years.

• The residues in honey tend to be connected to those used in oilseed rape fields.

• Clopyralid and glyphosate residues prevailed in honey samples.

• The concentrations found do not pose any health risk to consumers.

• The concentrations probably do not cause any acute toxicity to honey bees.

Abstract

Pesticide treatments before and during the flowering of honey bee forage crops may lead to residues in honey. In northern regions oilseed rape belongs to the main forage crops that is mostly cultivated by means of intensive agriculture, including several pesticide treatments. However, in addition to the focal forage crops, pesticides from non-forage crops can spread to wild flowers around fields, and thus the residues in honey would reflect the whole range of pesticides used in the agricultural landscape. The aim of our study was to clarify which currently used pesticides are present in honey gathered from heterogeneous agricultural landscapes after the end of flowering of oilseed crops.

Honey samples (N = 33) were collected from beehives of Estonia during 2013 and 2014, and analysed for residues of 47 currently used agricultural pesticides using the multiresidue method with HPLC-MS/MS and GC-MS and a single residue method for glyphosate, aminopyralid and clopyralid. Residues of eight different active ingredients with representatives from all three basic pesticide classes were determined. Although no correlation was detected between the cumulative amount of pesticide residues and percent of oilseed crops in the foraging territory, most of the residues are those allowed for oilseed rape treatments. Among all pesticides, herbicide residues prevailed in 2013 but not in 2014. Despite the relatively small agricultural impact of Estonia, the detected levels of pesticide residues sometimes exceeded maximum residue level; however, these concentrations do not pose a health risk to consumers, also acute toxicity to honey bees would be very unlikely.

Introduction

Using honey as natural food sets high demands on its quality. However, honey production occurs hand-in-hand with agricultural activities, and pesticide residues have been detected in honeys from several countries at varying levels, sometimes even exceeding the maximum residue levels (MRL) allowed (Souza Tette et al., 2016).

Pesticides can enter beehives via several routes. Hive treatments using medical products to combat honey bee parasites and pathogens bring about residues in wax and other bee products (Kujawski and Namieśnik, 2011, Nakajima et al., 2015). Honey bees collect pollen and nectar from treated crops: they might not avoid freshly treated fields even if the product used has been labelled as being repellent to bees (Karise et al., 2007). Foraging outside the fields may also result in contaminated food resource through spray drift from fields to wild vegetation (Long and Krupke, 2016). It has been convincingly demonstrated that pesticides used on fields can drift a long way to neighbouring areas (Krupke et al., 2012, Hladik et al., 2016, Long and Krupke, 2016), thus contaminating the pollen and nectar of wild flowers, which in turn may lead to contaminated honey production even in organic apiaries, as described in Italy (Chiesa et al., 2016). In addition to currently used pesticides, field soil tends to retain many chemicals used throughout (Kumar et al., 2016, Lozowicka et al., 2016, Zhang et al., 2016), and moreover, traces may occur in every plant product including nectar and pollen (Malhat et al., 2015, Chiesa et al., 2016).

Analyses of pesticide residues in honey have been carried out in several countries (reviewed by Souza Tette et al., 2016). An important set of studies analysed honey for contamination by organochlorines, many of which are banned (Panseri et al., 2014, Al Naggar et al., 2015, Chiesa et al., 2016). However, although this data is interesting, it does not lead to any understanding of the consequences of those pesticides used nowadays when pyrethroids and neonicotinoids are becoming more and more popular. We know of no up-to-date survey on honey contamination by a broader spectrum of currently used pesticides. For Nordic areas, there is only one study which analyses honey and this considers the presence of four pesticide residues of neonicotinoid insecticides (Laaniste et al., 2016), where it is shown that the frequency of pesticide residues in honey was correlated with the year-wise increase in product importation.

As in other Nordic countries, the pesticide input into Estonian agriculture is relatively low, being less than 1 kg ha⁻¹ of utilised agricultural area (Eurostat, 2015), whereas in most Central European countries like France, Germany, Belgium and the Netherlands, the amount of pesticides sold is over 2 kg ha⁻¹. In Estonia, more than half of the country's territory is covered with forests and other wooded lands (Eurostat, 2015). This, and the low pesticide input, makes people assume that the nectar from wild and presumably unpolluted flowers should dilute the nectar from cultivated plants to a level where residues are no longer detectable.

Estonian honey is polyfloral; however, Brassicaceae pollen belongs to the four most common plant species found from honey samples (Puusepp and Koff, 2014). Most of the Brassicaceae pollen probably belongs to cultivated oilseed crops, from which most are grown by means of conventional agricultural methods. The pesticide treatment suggested for oilseed rape starts with soil preparation using herbicides, followed by sowing dressed seed to protect the seedlings against fungal diseases and flea beetles. Later, several treatments against other insect pests and phythopathogens are suggested. As pre-harvest treatment, glyphosate is suggested to reduce harvesting losses. Due to the large content of Brassicacea pollen in Estonian honey (Puusepp and Koff, 2014), we hypothesize that the possible residues found in honey reflect those used in oilseed rape agrotechnology. However, there is evidence that different groups of pesticides are correlated differently with forage crops in foraging ranges of honey bees (McArt et al., 2017). Therefore, we aimed to clarify which of the currently used 50 pesticides are present in honey gathered from heterogeneous agricultural landscapes after the flowering of oilseed crops.