On mainland Europe, 18 people have died and 1,500 fallen ill with E.coli poisoning linked to salad produce, and now the bug is feared to have spread to Britain, with at least seven people infected.

The culprit was originally thought to be organic cucumbers exported from Spain to Germany, but now officials have admitted that they don’t even know which salad item caused the outbreak.

But that’s not the only reason to be vigilant.

Sewage contamination

Salad is full of water, which is why it has so few calories. Cucumbers contain a whopping 96 per cent water, while in lettuce it’s 95 per cent, so to grow these plants requires a constant and plentiful water supply.

Herein lies the problem: if there’s any contamination to that water by potentially lethal bugs such as E.coli, listeria, salmonella and campylobacter (all found in the gut of farm animals), they won’t just reach the plants, but can live in the salad cells until we eat them. Even washing won’t help.

Terrifyingly, all it can take is cross-contamination from a nearby field or factory. It is perfectly legal to spread poultry manure, pig slurry and even human waste as fertiliser (it’s cheap and easy to come by and therfore popular with farmers), provided it has been treated (i.e. composted for a couple of years).

This process is supposed to kill off any dangerous bacteria or pathogens. But if manure that hasn’t been left long enough, or untreated animal waste, gets accidentally washed into a ground water supply by rain, it can contaminate an entire salad crop — and often does.

Toxic pesticides

Most of the salad that reaches our plate is grown in heated polytunnels or glass houses so we can get our favourite items all year round. But since the growth in popularity of polytunnels in the Nineties, the level of pesticides on our salads has shot up.

In open fields, a harsh winter would kill off any insects and mould that could threaten crops. But in warm, moist polytunnels, pests thrive — so farmers have to spray higher amounts of insecticides and fungicides.

Today, one in four British lettuces is contaminated with the chemicals — which get into the cell structure of the leaf (so you can’t wash it off).

Spinach and red peppers are also badly affected. This is a serious worry, as some foreign farmers still (illegally) use banned chemicals which have been deemed dangerous to human health, or spray pesticide too close to the harvest. If you ingest these, you could end up with pesticide poisoning, which can lead to nervous system damage.

Even if this doesn’t happen, regular salad eaters are taking in a cocktail of pesticides over time. Not enough research has been done into the effect of this drip-drip exposure — but it’s certainly not good for us.

Dirty washing

Nowadays, supermarkets like their salad to look pretty, so it’s all washed. But this isn’t as healthy as we think, as it’s common practice to add a disinfectant — chlorine — to the water, supposedly to keep the water clean and kill off any bugs.

This practice gives factories a false sense of security: just dunking a cucumber in chlorine wash will not kill E.coli — in fact, some research shows that the bug is resistant to the chemical. Also, the water is often not changed enough, thereby reducing any sanitising effect.

Even if the chlorinated water is fairly clean, the chemical itself actually reduces the nutritional value of the salad, reducing levels of its vitamins A, C, E and folates (which can boost the brain and bones) — surely one of the reason we eat greens in the first place. Plus, it gives the leaves a nasty taste.

The best way to avoid the problem is to buy unprepared salad (e.g. whole lettuces) — and always wash it thoroughly yourself.

Poor factory hygiene

Have you ever stopped to think about who is picking your tomatoes, washing your cucumber or chopping your lettuce?
Both in this country and abroad, it’s almost always underpaid migrant labourers.

It’s hard, thankless work that most people avoid and, thanks to supermarkets squeezing growers to cut their costs, it’s very badly paid.

When exploited people are working in polytunnels and factories in poor conditions, it’s more than likely that corners will be cut and protocol ignored, from ensuring water supplies are clean to washing hands before work.

So it’s no wonder that hygiene in these environments can fall below standard and errors occur.

Gases in bagged salad

On our supermarket shelf, we’re inundated with ‘pillow packs’ — bags of puffed up, chopped up, ‘ready-to-eat’ salads which we buy by the basketful to save time and effort.

The gas inside the bag is what the food industry calls ‘modified atmosphere packaging’. What that means is that the oxygen in the air inside the bag is sucked out, and replaced with pure carbon dioxide.

Without the oxygen, which helps the decomposition process, the food looks fresh for longer.

This is a great boon for retailers but, like the chlorine wash, it negatively affects the nutritional value of the salad — in particular, its vitamin C content, although this is hotly disputed by salad companies.

Week old produce

That fresh-looking produce we see at the supermarkets is not as new as you might think.

During research for my new book, What (And What Not) To Eat, I discovered that farmers who supply supermarkets have to deal with quite unpredictable ordering.

For example, if it’s a hot weekend, the stores bump up their orders of salad. This means that the lettuce, cucumbers and tomatoes have to be picked in advance, prepared, packaged, and kept deep-chilled, all ready to send out to supermarkets if suddenly required.

But if the orders do not come in, a backlog soon builds up and before you know it the salad that arrives at your supermarket shelves is seven to ten days old before you take it home.

Each day’s delay will mean a reduction in nutritional value and ageing can even cause a bitter taste in the food.

Try a freshly grown lettuce from someone’s garden — you’ll notice the difference in the sweetness of the produce and you’ll be getting a bigger shot of vitamins.

P.S. And it harms the environment

Did you know that as well as potentially damaging our health, the salad industry is also damaging our environment?

Due to our growing obsession with having every salad crop every day of the year (and supermarkets often failing to use local growers even when their crop is in season), we import huge amounts of produce. This has to be trucked, shipped or — worse still — airfreighted, which leaves a high carbon ‘foodprint’.

Most of our peppers and tomatoes come from Holland, cucumbers from Spain and avocados as far afield as South Africa, the U.S. and South America. Not only is there pollution from the fuel, but keeping them cold is hugely energy-intensive.

The solution? Choose seasonal, local produce when you can.