As a journalist, I have just one thing to add to the discussion. Even though I respect and understand the (many many times difficult) work of a tabloid reporter, I do believe that every journalist must be prudent when he or she conveys the notion of an imminent risk. And, in my opinion, tabloids often fail to do so. (It might be argued that if they didn’t there would be a shortage of eye-catching headlines.)
When I read that nanoparticles can worm their way into my brain or kidneys, I want to know how likely it is to occur. I was not at that House of Lords event and Lord Krebs is not a friend of mine. I cannot obtain this information myself. As a reader, I count on the reporter to tell me that. I also count on him or her to explain me that, at this stage, the risk is not measurable, if it is the case. I can even cope with uncertainty but I want storytellers to explain me that, and also to present me comparison terms. They cannot simply leave me scared about microscopic and insidious compounds that can seize my liver like in an Alien film.
I am also told that the consequences are unknown. This is to say, I imagine, that the consequences can be good, bad or innocuous. We simply don’t know. As a reader, I am inclined to believe they are bad *precisely* because they are unknown – there is nothing more unsettling than facing something I cannot name, measure or control. The judgment I make toward this ‘grey goo’ is connected with my sensitivity. Human perception of risk is complex and may vary through time and according to context and circumstances. Nothing wrong with that. But there *is* something wrong when I feel that the same text which brought this new risk into my life (into my bowels!) is also adding up anxiety to my perception of the very same risk.
As a reader, I want somebody who helps me to establish a rational frame in the risk scenario. As a reader, I want the reporter to quote what independent expertises have to say about these risks. And, finally, as a journalist, I think it is part of our job to explain once and again what do we really talk about when we talk about risk. Writing that zero risk simply does not exist is a good start off.

P.S. This discussion makes me think about something I experienced many years ago back in Ispra (Italy), where I was attending to a meeting on food packaging at the Joint Research Centre (JRC). We, journalists, were very interested in molecular migration from plastic packages to food. We wanted to know how those molecules could harm us and what is their level of toxicity.
The answers provided by the JRC representatives were not vague but not precise either. They were giving general answers to general questions. It would always depend, they explained, on the package (what material the container was made of) and its content (you don’t heat orange juice in microwaves, but you might want to eat your soup nice and warm). It would also depend on the correct use of the packages (some are not prepared to be reheated or used as a Tupperware, for example).
I realized then that it would be difficult to find the definitive and answer we were looking for. It became clear that part of our stories would have to be filled with the uncertainties themselves – and it constituted a problem for me, I could see no story without a good quote on how risky those evil plastics were. It took me ages to accept that we could take advantage of this absence of “one-answer-fits-all” and invite the reader, for instance, to think about why our food *has* to be sold in plastic packages (full of molecules ready to migrate to our bodies and disrupt our endocrine system, one might say). Only when I began to explore this new angle I started to get juicy answers considering alternatives (plastic versus glass), pros and cons of active packaging and even risk assessment in hypothetical scenarios. Maybe I was too keen on zero-risk answers to have chosen this path before.

The “emotional hysteria” is a significant issue, and I was partly poking readers to see whether anyone would come back at me on this. Would love to know how people think headlines – and the emotive responses they elicit – alter perceptions and attitudes (and whether there is hard research here, or just anecdotes).

However, I wonder if it is actually the emotional hysteria of the headline that will stick in people’s minds more than the copy below. Interesting to see what follows if anything. The comments below give us a taster of what to expect, but again, most have perfectly valid points, if a little OTT.

Also in Fiona’s defence it’s usually the subs who create the headlines and ‘spice things up’ a bit. So it looks like she may have written a balanced piece as you say which was tarted up to suit the Daily Mail USP.