Ethylene is a plant hormone, and might be expected to affect plants at low concentrations. It is used commercially at relatively high concentrations to regulate flowering and fruiting. For reviews see Mattoo & Suttle(1991), Abeles(1992), Cape(2003), Collins & Bell(2002). Direct effects have been observed at concentrations of 100 nl/l (ppb), with a threshold response at 10 nl/l. Ethylene is emitted in vehicle exhausts, and from factories that produce polyethylene. Effects (leaf epinasty -increased growth on the upper surface of a leaf, causing it to bend downward) have been observed in the field downwind of such factories (Tonneijk et al., 1999).
There is little quantitative information available to evaluate the likelihood of effects on different plant species under field conditions. Vegetation is exposed to large concentrations (up to 100 nl/l as hourly average) on roadside verges and close to industrial sources, where short-term exposure to high concentrations may be possible as a result of a leak or accident.
Ethylene concentrations have been measured in urban air in the UK. (http://ariadne.aeat.co.uk). The largest hourly average concentration measured in the UK was in Middlesbrough (over 800 nl/l), although annual average concentrations were only 4 nl/l at that site. The largest hourly average concentration measured at a rural site was 12 nl/l.
|Critical Load/ Level|
No estimate available