Oilseed rape pollen
Oilseed rape pollen grains are roughly spherical with a geometric diameter of about 25μm.
Oilseed rape is an entomophilous (insect pollinated) crop and as such airborne pollen dispersal is considerably less than wind pollinated plants like grass. However, a percentage of pollen will indeed become wind-borne and will therefore both contribute to crop pollination and be dispersed down-wind of the rape fields.
Whilst it is true that wind-borne oilseed rape pollen doesn’t really travel too far from the field due to its size (PM25) and sticky external coating. It is equally true to say that wind-borne oilseed rape pollen can and does disperse fairly widely into the environment.
Rape pollen has been recorded in a pollen trap some 15km from the nearest field (Caulton E. The Scottish Centre for Pollen Studies, private communication to McGorum & Dixon). Parratt also confirmed in a private communication to McGorum & Dixon that his researchers had confirmed using pollen traps, that oilseed rape pollen had travelled 1.7km from the field. In a separate report published in Clinical & Experimental Allergy, Hemmer advises; in the centre of Vienna, several kilometres away from rape fields, the daily maxima was measured and recorded as around 30 grains/m3 24h.
Timmons et al. (1996) reported that in their study characteristic pollen dispersal lay between 128 and 172 metres from the edge of the field, with 95% confidence. The authors suggested that the dispersal distance could be explained, at least in part, by the use of commercial sized fields, 24-hour monitoring and widely spaced sampling sites. They concluded from their results demonstrated that quantities of rape pollen will travel over large distances.
In contrast (McCartney & Lacey, 1990), using a mathematical model based upon pollen trap data, predicted that more than 60% of pollen lost from an oilseed rape crop would still be airborne 100m downwind of the crop. The concentration at the ground at this distance, however, would only be 2 to 10% of the value at the edge of the crop. The conclusion from this work was that, although large amounts of pollen are released into the air from flowering oilseed rape crops, it seems unlikely that windborne pollen could play a significant role in cross-pollination at distances greater than a few tens of metres from that crop.
In terms of trying to establish a fair and reasonable assessment of oilseed rape pollen dispersal (in the absence of agreement within the scientific community) in respect of risks to public health from oilseed crops planted in close proximity to residential areas. The author believes it is reasonable to assume that windborne oilseed rape pollen will be dispersed within a 1km zone emanating from the edge (nearest to residential area) of the respective rape field.
It is also fair to say that the pollen concentration will reduce substantially over distance. Those living closest to the rape fields being exposed to the higher concentration of airborne oilseed rape pollen.
Author - Armitage; copyright 2007