a while ago i bought my grandson, a toddler, a bright yellow wooden racing car, for just 99 cents. but then i happened to read that lead in paint makes colors (particularly yellow and red) brighter and last longer; because lead costs less than alternates, cheaper toys are more likely to contain it. i have no idea if the sparkling yellow paint on this toy car harbors lead or not-but now, months later, that sporty racer sits atop my desk. i never gave it to my grandson.

every item we buy has a hidden price tag: a toll on the planet, on our health and on the people whose labor provides those goods. each man-made thing has its own web of impacts left along the way from the extraction or concoction of its ingredients, during its manufacture and transport, through its use in our homes and workplaces, to the day we dispose of it. these unseen impacts are incredibly important. for instance, an ingredient in sunscreen primes the growth of a deadly virus in coral reef. four thousand to 6,000 metric tons of sunscreen wash off swimmers each year worldwide. the dangers are greatest, of course, where the most swimmers are drawn to the beauty of coral reefs.

our inability to instinctively recognize the connections between our actions and the problems that result from them leaves us wide open to creating the dangers we decry. our brains are exquisitely attuned to pinpoint and instantly react to a fixed range of dangers, such as snarling animals. but our perceptual system misses the signals when the threat comes in the form of gradual rises in planetary temperature, or minuscule chemicals that build up in our body over time.

fortunately, the past decade has witnessed the emergence of industrial ecology, a discipline that uses life-cycle assessment (or lca) to deconstruct any manufactured item into its subsidiary industrial processes and their myriad ecological impacts with great precision. an lca tracks, say, a glass jar from the initial extraction of the silica from sand through the 48 hours of cooking at 2,000 degrees fahrenheit all the way through its final disposal. that lca tells us that heating the furnace accounts for 16 percent of glassmaking's negative impacts; the chemicals released into the air from the glass factory run from relatively high levels of carbon dioxide to trace amounts of toxic metals like cadmium.

lcas can provide the raw data that let us be ecologically intelligent about what we buy, whether what we care about is the impact on polar bears, or on that especially prized part of nature, our bodies. but lcas are highly technical, the terrain of industrial engineers. here's the good news: if i were shopping for kid-safe toys now, i could use goodguide, a neat piece of free software that i downloaded the other day on my iphone. goodguide analyzes the results from about 200 technical databases, several of them industrial lcas, and offers them in an easy-to-use summary.

goodguide rates toy cars not just on whether they contain lead, but also other toxic ingredients like mercury, pvc and a list of heavy metals. it also rates them on their environmental impact and the company's social performance, such as whether suppliers use sweatshops.

as shoppers, we finally have sound ways to gauge the hidden consequences of what we buy. by switching to brands that have better profiles, we can shift market share toward ecological benefits. as we tell our family, twitter our friends and post on facebook what we have learned, the power of our individual decision multiplies.

virtually everything we make today was invented or designed in a more innocent time, one when shoppers and industrial engineers alike had the luxury of paying little attention to the adverse impacts of what was made. instead they were understandably pleased by the benefits: cheap, malleable plastics made from a seemingly endless sea of petroleum; a treasure chest of synthetic chemical compounds; lead powder to add luster and life to paints.

they were oblivious to the costs to our planet and its people of these well-meaning choices. now that those costs are clear, we need to reinvent just about everything. that vast innovative opportunity gets richer if each of us votes with our dollars. then doing good becomes synonymous with doing well.

（adapted from ecological intelligence: how knowing the hidden impacts of what we buy can change everything. copyright ? 2009 by . published by broadway books, a division of random house, inc.）