San Diego is justifiably very proud of its beautiful parks and beaches. However, there is one aspect of its public environment that remains highly polluted. Parks and other open spaces accumulate weeds, and San Diego continues to spray large amounts of dangerous chemicals to kill these weeds throughout the city and in schoolyards.

The most widely used weed killer or herbicide is Roundup, a mixture of the plant toxin glyphosate and other chemicals called surfactants that are required for the glyphosate to kill plants. Glyphosate itself is a potential carcinogen as determined by the World Health Organization and numerous scientific publications.

The ability of Roundup to cause cancer was substantiated in three recent jury trials in which its major producer, Monsanto, now a subsidiary of Bayer, was found guilty of knowingly selling a dangerous product. The latest award was over $2 billion. These trials brought to light documents showing that Monsanto manipulated both toxicity studies and the government approval process to allow the sale of Roundup.

Glyphosate is the most widely used agricultural chemical in human history, and almost every individual in this country has it in their bodies. Glyphosate-containing herbicides have also been implicated in causing diseases of the intestine, liver and kidney. Recently, glyphosate exposure was linked to human liver fibrosis in a study from the University of California, San Diego.


Glyphosate is required for productively growing most genetically modified (GM) crops, and is also a major contaminant of the majority of grains such as wheat, oats and barley where it is used to dry the crops to speed up harvesting. Therefore, glyphosate is in most cereals, breads and beers.

While we can avoid most food-borne glyphosate-containing herbicides by not eating GM foods and sticking to an organic diet, we cannot easily avoid environmental exposure unless these herbicides are not used. The chemicals in glyphosate-based herbicides like Roundup are long lived in the environment. They break down slowly and remain on the plants and in the ground for a long time. They can also migrate into the air with dust or in the misty conditions that are frequent occurrences in San Diego. Indeed, a significant amount of human glyphosate exposure is from the air.

The most efficient way to reduce human exposure to chemical herbicides is to ban them. Multiple countries, states, cities and school districts have either outright banned glyphosate products or severely limited their use. The European Union is developing plans to eliminate glyphosate use within the next few years. Many countries have already banned retail sales of Roundup and its use as a pre-harvest drying agent.

In California, over 40 cities and counties have either restricted or completely banned the use of glyphosate and similar chemical herbicides on their properties, including Los Angeles County and the city of Irvine. The president of the University of California, Janet Napolitano, recently banned the use of glyphosate-based herbicides on all UC campuses. Because other types of herbicides also contain compounds that are toxic to humans, several jurisdictions have wisely banned all chemical herbicides.


The political leaders of the city of San Diego and the members of San Diego Unified School District Board of Trustees certainly understand that the health and safety of citizens and students is their primary responsibility. Because of the preponderance of evidence showing that Roundup is a carcinogen, it is clear that it and related chemical herbicides are hazards to public health. Based upon the success of recent lawsuits, its continued use will also pose liability concerns for the city.

Herbicide spraying in public spaces, parks, playgrounds and schools is not necessary, and should be halted immediately. Non-toxic alternatives are now available. All educational facilities should follow UC’s example and do the same. In addition, to reduce personal exposure to glyphosate, individuals are advised to avoid all genetically modified food products and eat and drink organic when possible.

Numerous scientists like myself have been trying to make the public aware of the health hazards associated with glyphosate-based herbicides for many years. Because more of the facts about their toxicity have recently become public knowledge through evidence presented in courts of law as well as scientific publications, now is the time for San Diego to join other major cities and school districts and ban the use of Roundup and all chemical herbicides. Call your City Council member and school board representative and ask them to get this done immediately.

Schubert, PhD, is a professor at Salk Institute for Biological Studies.