Cooking up a cancer panic

Here's a quick test. Which of these two statements is true:

A.Scientists  in Norway have found that potentially dangerous fumes from pan-frying meat with gas were well below that country’s occupational health limit.
B. Scientists in Norway found that pan-frying meat with gas may be worse than electricity for raising cancer risk.
The answer is: both. Indeed, they are based on findings from the same research paper. But there are no prizes for guessing which made national news on 18 February. The Independent reported "Cooking with gas raises risk of lung cancer", the Daily Mail with '"The 'cancer risk' of frying steak on a gas hob" and The Daily Telegraph with  "Frying steak on a gas hob 'may increase risk of cancer'".
Perhaps we should not be too harsh on journalists with deadlines looming – except they had been spoon-fed this story two days earlier by a press release from Occupational and Environmental Medicine, a BMJ Specialist Journal, using the headline in statement B above. It was  summarising a paper by scientists working at the Norwegian University of Science and Technology in Trondheim who had measured exposure to polycyclic aromatic hydrocarbons (PAHs), mutagenic aldehydes and particulate matter during pan frying of beefsteak.
The authors found that the level of naphthalene, one of the nastiest of the PAHs, was in the range 0.15-0.27µg/cubic metre. They conceded that this was “far below” Norway's occupational exposure limit of 40µg/cubic metre (there is no exposure limit in the UK).
The researchers also found low levels of higher aldehydes and ultrafine particles, some of which are known to be mutagenic or otherwise harmful, while others represent as yet unquantified health risks. On this basis, they warned that “cooking fumes should be reduced as much as possible”.
For the press, this was enough. If they mentioned the fact that exposure was well below recommended levels, it came some way after sensational headlines and opening paragraphs. This skewed coverage provoked both the Behind the Headlines team at NHS Choices and Cancer Research UK into their own attempts to put the risk into perspective.
“Although The Daily Telegraph and the Daily Mail stated that the amounts of the chemicals produced during cooking were within safety limits, this fact was not adequately emphasised in their reports and their coverage tended to sensationalise the story” said Behind the Headlines. “This research looked at the chemical composition of cooking fumes. It did not look at the health consequences of exposure to the chemicals produced by cooking, as could be assumed from reading the media reports'
Cancer Research UK said that the low levels of cooking fumes found in UK kitchens are unlikely to affect people's risk of cancer. Ed Yong, head of health information at CRUK, said that people “shouldn't worry unduly” if they have a gas hob.
 “The bottom line is that as long as you've got decent ventilation, the type of hob you use is unlikely to matter”' he said, adding: “The highest levels [of naphthalene – a banned chemical] were found in meat fried with margarine on the gas hob. However, these levels were still 150 times lower than the accepted safety thresholds.”
There is an extensive and authoritative scientific literature about nasty chemicals in cooking fumes. Professional chefs in poorly ventilated kitchens, particularly in Asia where cooking with hot oil is more popular, appear to be more susceptible to lung cancer.
But as Behind the Headlines pointed out, the Norwegian group did not address cancer risks of their findings. Nor did they discuss in any detail the background levels of the potentially harmful chemicals that they measured. These are known to be present in low concentrations as pollutants in air, water, food and soil.
Naphthalene, for example, has been described as “an ubiquitous environmental pollutant” (International Archives of Occupational and Environmental Health, (2003) 76: 556–576), while a report published in 2003 by the US Environmental Protection Agency ('Health Effects Support Document for Naphthalene') claimed: "Estimates for daily intake of naphthalene via the diet ranged from 40.7 to 237 ng/kg-day for a 70 kg adult and 204 to 940 ng/kg-day for a 10 kg child. Comparison of the available data indicates that, based on rough estimates of average intakes for naphthalene, most exposure occurs through inhalation. Estimated intakes from air are approximately 5 to 45-fold greater than those from food and water."
It would seem that in any event our daily exposure to naphthalene in the air is significantly higher than that measured in the Norwegian study, whether or not we are frying steak. 
Benzo(a)pyrene (BaP) is even nastier than naphthalene. Produced by incomplete combustion, it is found in fumes from diesel engines, cigarettes, and wood stoves. Since the Norwegian paper was written, the carcinogenic risk of Benzo(a)pyrene (BaP) has been raised by the International Agency for Research on Cancer from Group 2 "probably carcinogenic to humans" to Group 1 "carcinogenic to humans".But the level found in the Norwegian study was still about ten times lower than the occupational exposure limit set by some countries:
"BaP was detected in two of the 17 samples, both collected during frying with margarine on the gas stove" the Norwegian paper says. "The OEL for BaP in some countries is 2µg/cubic metre (Austria, Canada and Sweden) and the measured level was less than one tenth of this OEL."