Tomatoes, Salmonella, and Sewage
With consumers nationwide toppling over from eating tainted tomatoes, the media has focused on the question of where in the world the salmonella-infected tomatoes come from. It seems that all the167 cases of salmonella that have so far surfaced bear the same genetic fingerprint, indicating a common point of origin -- and right now, all fingers point toward Mexico. Not to California, Guatemala, North Carolina, nor Hawaii, nor to other places that distribute tomatoes here -- and that's causing much agitation among Mexican growers.
According to an AP article, Manual Tarriba, who heads the state Tomato Growers Association in Sinaloa, says that U.S. health officials have presented no proof that the contaminated tomatoes are from Mexico. "Even if it were to be determined that Mexican produce (is) the origin of any of these cases, the FDA has to determine if the problem came from the raw product itself or was acquired during the transportation, distribution, storage or cooking processes," said Ricardo Alday, a spokesperson for the Mexican embassy.
Whether or not the tomatoes come from Mexico, here's the thing. Farmers in Mexico typically irrigate with treated sewage. Although wastewater irrigation for unprocessed crops has been outlawed in most modern nations, one tenth of the world's crops still are irrigated with sewage, according to a 2004 article in New Scientist. This includes liquefied substances flushed from domestic toilets, baths, and sinks; any liquid waste generated from manufacturing and industrial operations; and the runoff from gutters, roofs, streets, and so on. At least in Mexico, the sewage goes through a treatment process that supposedly removes pathogens and poisons and renders it safe, but in developing countries across Asia, Africa, and Latin America, in India, Pakistan, and China, it's often raw, untreated sewage that gets used.
Why do farmers use sewage? Because it's cheap, and available, and crops do grow well in the sewage-soaked soil. Wastewater contains nitrates and phosphates that plants love. In fact, crops watered with effluent typically don't need fertilization, which saves huge amounts of money for the growers in poor nations. Unfortunately, wastewater also typically contains pathogens and toxic industrial contaminants delivered directly via sewage pipes to the fields.
When farmers rely on treated wastewater to irrigate crops, they assume that the water will, in fact, get treated as prescribed, and that water quality will be monitored--that, in fact, they aren't applying contaminated water to crops. But sometimes the process breaks down, which is why using wastewater for crops that get eaten raw is risky business. Even if the crops don't end up infected with something like salmonella, sewage contains high concentrations of various viruses, bacteria, protozoa, and helminthes, as well as heavy metals and industrial toxins. For instance, a study of wastewater used for irrigation in Punjab, India, found concentrations of lead (Pb), chromium (Cr), cadmium (Cd), and nickel (Ni) from 18 to 2200 times higher than in water from hand-pumps or wells.
The irony here is that crops irrigated with sewage still can be sold as organic. So the organic tomatoes from Mexico that looked so good might actually have a coating of invisible sewage sludge that will literally come back to bite you. In other words, it pays to know where your food comes from and how it gets produced and shipped to you, even if it's sold at your favorite health food store. It also pays to know that according to the World Health Organization, wastewater use will become increasingly necessary as water shortages and increasing demand for food affect the world's population.
By the way, washing won't help. The problem is that since these contaminants aren't just on the surface of the plant--since they're in the irrigation water--they get sucked up inside the plants. You can scrub all you want, but nada. Yes, cooking helps a little. If you cook your vegetables long enough, you can kill the bacteria inside. But then you're left with nutritionally dead, enzyme devoid, tasteless mush. And you still have all of the heavy metals to deal with.
Hey, I'm not knocking Mexico here. Farmers there have made great strides in eliminating toxic pesticides from their growing cycle over the last 20 years. But using treated effluent for irrigation carries unnecessary risk. And so, I suggest that you be cautious about purchasing produce imported from regions with questionable agricultural practices. Maybe grow your own. Or just buy at local farmer's markets from growers whose growing and handling methods you know and trust.