THE WIKIPEDIA PROBLEM

In December, Nature published the findings of its expert-led, peer reviewed investigation/comparison of Wikipedia and Encyclopedia Britannica, concluding "the difference in accuracy was not particularly great"... The difference in accuracy was in fact, great, with Wikipedia having 162 errors over 42 articles compared to Britannica's 123. (The Wikipedia analysis is here.)

Britannica was not happy with the Nature investigation and has now responded with its own analysis:

We discovered in Nature’s work a pattern of sloppiness, indifference to basic scholarly standards, and flagrant errors so numerous they completely invalidated the results. We contacted Nature, asking for the original data, calling their attention to several of their errors, and offering to meet with them to review our findings in full, but they declined.

As a regular user of both Wikipedia and Britannia - actually, I go to Wikipedia much more often than Britannica, which requires log-in - I'm going to side with the latter on this: Wikipedia is not to be trusted, ever. A quick comparison follows; decide for yourself which you should trust.

Agent orange is included as part of the Nature investigation. The Wikipedia agent orange article is quite long and sensational. Excerpt:

The National Toxicology Program has classified TCDD to be a known human carcinogen, frequently associated with soft-tissue sarcoma, Non-Hodgkin's lymphoma, Hodgkin's disease and chronic lymphocytic leukemia (CLL). 2,4,5-T has since been banned for use in the US and many other countries...

Diseases associated with dioxin exposure are chloracne, soft tissue sarcomas, Hodgkin's disease, and non-Hodgkin's disease. Diseases with limited evidence of an association with Agent Orange are respiratory cancers, prostate cancer, multiple myeloma, Porphyria cutanea tarda (a type of skin disease), acute and subacute transient peripheral neuropathy, spina bifida, Type 2 diabetes, and acute myelogenous leukemia found only in the second or third generation. Diseases with inadequate or insufficent evidence of an association are hepatobiliary cancers, nasal or nasophargyngeal cancers, bone cancer, female reproductive cancers, renal cancer, testicular cancer, leukemia, spontaneous abortion, birth defects, neonatal or infant death and stillbirths, low birth weight, childhood cancers, abnormal sperm parameters, cognitive neuropsychiatric disorders, ataxia, peripheral nervous system disorders, circulatory disorders, respiratory disorders, skin cancers, urinary and bladder cancer. Diseases with limited or suggestive evidence of no association are gastrointestinal tumors such as stomach cancer, pancreatic cancer, colon cancer, and rectal cancer, and brain tumors.

The Britannica article is elegantly concise – it's subscription only; here's the whole thing so you can compare:

Agent Orange - mixture of herbicides that U.S. military forces sprayed in Vietnam from 1962 to 1971 during the Vietnam War for the dual purpose of defoliating forest areas that might conceal Viet Cong and North Vietnamese forces and destroying crops that might feed the enemy. The defoliant, sprayed from low-flying aircraft, consisted of approximately equal amounts of the unpurified butyl esters of 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T). Agent Orange also contained small, variable proportions of 2,3,7,8-tetrachlorodibenzo-p-dioxin—commonly called “dioxin”—which is a by-product of the manufacture of 2,4,5-T and is toxic even in minute quantities. About 50 million litres (13 million gallons) of Agent Orange—containing about 170 kg (375 pounds) of dioxin—were dropped on Vietnam. Agent Orange was one of several herbicides used in Vietnam, the others including Agents White, Purple, Blue, Pink, and Green. The names derived from colour-coded bands painted around storage drums holding the herbicides.

Among the Vietnamese, exposure to Agent Orange is considered to be the cause of an abnormally high incidence of miscarriages, skin diseases, cancers, birth defects, and congenital malformations (often extreme and grotesque) dating from the 1970s.

Many U.S., Australian, and New Zealand servicemen who suffered long exposure to Agent Orange in Vietnam later developed a number of cancers and other health disorders. Despite the difficulty of establishing conclusive proof that their claims were valid, U.S. veterans brought a class-action lawsuit against seven herbicide makers that produced Agent Orange for the U.S. military. The suit was settled out of court with the establishment of a $180,000,000 fund to compensate some 250,000 claimants and their families. Separately, the U.S. Department of Veterans Affairs awarded compensation to about 1,800 veterans.

Wikipedia's obvious emphasis on points scoring is the main difference between the two – its a matter of emphasis linked to political ideology. This becomes even more obvious if the Wikipedia and Britannica dioxin articles are compared. Here are some Wikipedia dioxin excerpts:

Dioxins are also in smoke from typical cigarettes, those with chlorine-bleached paper and residues of many chlorine pesticides. Dioxin in cigarette smoke was noted as "understudied" by the EPA in its "Re-Evaluating Dioxin" (1995). In that same document, the EPA acknowledged that dioxin is "anthropogenic" (man-made, "not likely in nature"). Dioxin cannot come from the tobacco or any natural plant. Since then, the USA classified dioxin as a Known Human Carcinogen, and the USA signed the Stockholm Convention on POPs to globally phase out dioxin and 11 other of the worst industrial pollutants. Nevertheless, chlorine tobacco pesticides and chlorine-bleached cigarette papers remain legal, with no warning required to consumers.

Dioxins are present in minuscule amounts in a wide range of materials used by humans — including practically all substances manufactured using plastics, resins or bleaches. Such materials include tampons, and a wide variety of food packaging substances. The use of these materials means that all modern humans receive (at least) a very small daily dose of dioxin—however, it is disputed whether such exceptionally tiny exposures have any clinical relevance. It is even controversially discussed if dioxins might have a non-linear dose-response curve with beneficial health effects in a certain lower dose range, a phenomenon called hormesis.

The article emphasises evil corporations disregarding people's health, with this the ultimate example:

In 1963 a dioxin cloud escapes after an explosion in a Philips-Duphar plant (now Solvay Group) near Amsterdam. Four people died of dioxin poisoning, and 50 more suffer severe health problems. In the 1960s Philips-Duphar produced 2250 tonnes of 'Agent Orange' for the US Army.

Agent Orange and the evil US Army are gravy. But, the article offers no substantiation that the four claimed deaths resulted from dioxin exposure. In reality, the cause of death of the four Philips-Duphar workers is not clear; the four deaths should not have been included.

Oddly, the Wikipedia Dioxin article downplays the supposed health effects featuring so prominently in the Agent Orange article (see Agent Orange excerpt above):

Excessive exposure to dioxin may cause a severe form of persistent acne, known as chloracne. This is the only known direct result of dioxin exposure at levels below the lethal dose. Other possible effects may be
▪ Developmental abnormalities in the enamel of children's teeth.
▪ Damage to the Immune systems.
▪ Endometriosis
▪ Birth defects
▪ Diabetes
▪ And at least in laboratory animals, increased rates of liver and lung cancer are observed.

In contrast, the Britannica article is elegantly concise:

Dioxin - any of a group of chemical compounds that is an undesirable by-product in the manufacture of herbicides, disinfectants, and other agents. In popular terminology, dioxin has become a synonym for one specific dioxin, 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD).

In chemical structure, a dioxin (technically called dibenzo-p-dioxin) consists of two benzene rings connected by a pair of oxygen atoms. Each of the eight carbon atoms on the rings that are not bonded to oxygen can bind with hydrogen atoms or atoms of other elements. By convention these positions are assigned the numbers 1 through 4 and 6 through 9. The more toxic dioxins carry chlorine atoms at these positions, and the best-known one has chlorine atoms at the 2,3,7, and 8 positions. This isomer—2,3,7,8-TCDD—is extremely stable chemically. It is virtually insoluble in water and in most organic compounds but is soluble in oils. It is this combination of properties that allows this dioxin in soil to resist dilution with rainwater and causes it to seek and enter fatty tissue in the body if it is absorbed.

Dioxin serves no useful purpose but is formed as an undesirable by-product during the synthesis of 2,4,5-trichlorophenol and some other useful compounds. The chemical 2,4,5-trichlorophenol serves as a raw material for making the herbicides Silvex and 2,4,5-T (2,4,5-trichlorophenoxyacetic acid). The latter is a major active ingredient of Agent Orange (q.v.), a defoliant formerly used in Vietnam by the U.S. military and in the United States to kill unwanted vegetation. This 2,4,5-trichlorophenol is also used in the production of hexachlorophene, an antibacterial agent formerly used in deodorants and soaps.

The recognition in the early 1980s that residential sites at Times Beach and elsewhere in Missouri, U.S., had been contaminated by improper disposal of chemical wastes containing 2,3,7,8-TCDD led to intense public scrutiny of its possible toxic effects. Toxicologists mistakenly concluded from studies on laboratory animals that TCDD was one of the most toxic of all man-made substances and recommended that soil levels in excess of one part per billion might constitute a health risk to humans. It was known that TCDD could produce chloracne, a serious skin rash, but exposure to the chemical was also blamed for muscular dysfunctions, various bodily inflammations, impotency, birth defects, genetic mutations, and nervous system disorders. TCDD was also linked to various cancers.

Subsequent research, however, discounted most of these inferences, which were based on the effects of very high doses of TCDD on guinea pigs and other peculiarly susceptible animals. Among humans, the only disease definitely found related to TCDD is chloracne, which develops shortly after exposure to the chemical. Epidemiological studies on industrial workers exposed to TCDD over many years show that it has a weak carcinogenic effect at high-dose exposures and no effect whatsoever at low-dose exposures. In fact, normally occurring exposure to TCDD appears to be less of a carcinogenic risk than similar exposure to asbestos, radon, or cigarette smoke. Nor has any convincing evidence been found for the association of TCDD with other bodily disorders and defects in humans, including genetic mutations.

What toxicity TCDD does possess apparently derives from the chemical's ability to bind with a particular type of receptor protein inside some cells within the body. The resulting TCDD-receptor complex can enter the cell's nucleus and bind with its DNA, thereby disrupting the cell's machinery for producing proteins. The wide and rather puzzling array of toxic effects induced in animals by high levels of TCDD are apparently all receptor-mediated responses to that chemical. Such animals' immune systems are those most often affected, being apparently weakened or compromised by TCDD.

If you're looking for well written, well researched, well edited information intended for knowledgable laymen go to Britannica. If you want iffy information written and argued over by guys like this, go to Wikipedia.