When Is Something Toxic?

During the 18th century, a pale complexion was considered attractive and a sign of good breeding. To achieve their pallor, the members of King Louis XVI's court took arsenic, perhaps weekly. Although we consider arsenic to be highly toxic, neither King Louis nor his wife, Marie Antoinette, died of arsenic poisoning. Actually, even today some level of arsenic in the diet is considered necessary for good health.

In contrast, some chemicals we consider beneficial have caused death. Before packaging laws were enacted, aspirin, one of the safest and most versatile medicines, was responsible for poisoning many children. Table salt is a common and necessary part of our daily diet, and though it's not necessarily a substance one would consider a toxin, an accidental substitution of salt for lactose in baby formulas has caused fatal poisoning. (An adult would have to ingest close to a half cup {400 grams} to receive a fatal dose.)

The subtle difference, then, between a chemical and a poison is quantity. When considering acute toxicity (or sudden death from exposure to a chemical), it is the amount needed to induce sudden death that determines whether a chemical is considered poisonous. Safe doses are measured by a statistical standard known as Lethal Dose (LD).

Because this issue is important to us, we'd like to pause here to note that Seventh Generation neither conducts nor approves of animal testing under any circumstances. We believe there are better and far more humane ways to measure toxicity, and we employ these alternative methods when testing our own products. However, both the scientific community and the cleaning products industry as a whole rely on the LD standard almost exclusively, a fact which means that no one has ever created an alternative set of similarly comprehensive, animal testing-free data. Because the LD standard is the only way to illustrate several crucial points, we're forced to use it here in spite of our reservations. The good news is that this will only take a moment or two.

The LD standard is based on a benchmark called the LD50. The LD50 is the quantity of a chemical needed to kill 50% of the animals in a test group (usually mice or rats). Because larger animals require larger doses of a chemical to exhibit toxic effects (i.e., it takes more arsenic to kill an elephant than a mouse), the LD50 is measured as the weight of chemical in milligrams (mg) per kilogram (kg) of animal weight needed to cause death.

For example, the LD50 of arsenic trioxide (a common form of arsenic), when measured in rats, is 15 mg/kg. This means about 15mg (approximately 0.0005 oz.) would kill a one kilogram (2.2 lb.) rat. By comparison, 3,000 mg (approximately 0.1 oz.) would kill a 200kg (440 lb.) gorilla.

The LD50 of aspirin, measured in rats, is 1,500 mg/kg. This means 1,500 mg (0.05 oz.) would kill a 1kg rat, and 300,000 mg (10 oz., over half a pound) would kill the 200kg gorilla. The LD50 of table salt (also in rats) is 3,750 mg/kg. At this rate, it would take 750,000 mg (nearly a pound!) of salt to kill the same gorilla.

What's important to note is that it takes 100 times more aspirin than arsenic trioxide to cause acutely toxic effects in a given animal. In other words, arsenic trioxide is 100 times more toxic than aspirin. It takes more than twice as much salt to kill an animal as aspirin. Thus, salt is less than half as toxic as aspirin. Confused? Don't be. Just remember that almost everything is poisonous in some amount. The less of a chemical needed to cause acutely toxic effects, however, the more poisonous it is.