A student asked about the impact of Bt pollen on streams after reading Genetically Engineered Corn Could Harm Aquatic Ecosystems www.sciencedaily.comreleases200710071008171030.htm Is this a concern?

Expert response from Wayne Parrott

Professor, Crop Breeding and Genetics, University of Georgia

Tuesday, 17/11/2015 12:16

Bt is a protein derived from soil-dwelling bacteria. Its use is widespread in both organic agriculture, and genetically engineered agriculture, as it presents many advantages over the use of traditional chemical-based insecticides. Among these advantages is the fact any given type of Bt protein only targets a very limited group of closely related insects, and is harmless to everything else.

The particular report cited in the question is about a 2007 study that claimed that pollen from Bt corn plants was toxic to caddisflies. However, that study had several shortcomings. First, modern Bt corn plants do not contain toxic levels of Bt protein in their pollen. Secondly, the chemical composition of pollen can vary between different corn hybrids. Hence, toxicological studies must be done on the same corn hybrid that differs only by the presence of absence Bt. Otherwise, it is impossible to determine if any difference is due to a difference in chemical composition, or to the presence of a Bt protein. Finally, the dose makes the poison—a greater response to increasing amounts of a compound is considered to be the hallmark that something is really causing harm. Thus, if Bt proteins were really harming caddisflies, caddisflies fed greater amounts of Bt pollen should suffer more than those fed smaller amounts. Such a relationship was not observed. Importantly, harmful effects could not be detected when the study in the report was repeated in a stream rather than in a laboratory.

So far there is no hard evidence that Bt pollen can harm aquatic ecosystems. But, Bt can enter streams in other ways. It is naturally found in soils. Also, bits and pieces of Bt corn plants can get washed in to streams. Therefore, the topic continues to be studied to determine if harmful effects can be detected.

Expert response from Wayne Parrott

Professor, Crop Breeding and Genetics, University of Georgia

Tuesday, 17/11/2015 12:16

Bt is a protein derived from soil-dwelling bacteria. Its use is widespread in both organic agriculture, and genetically engineered agriculture, as it presents many advantages over the use of traditional chemical-based insecticides. Among these advantages is the fact any given type of Bt protein only targets a very limited group of closely related insects, and is harmless to everything else.

The particular report cited in the question is about a 2007 study that claimed that pollen from Bt corn plants was toxic to caddisflies. However, that study had several shortcomings. First, modern Bt corn plants do not contain toxic levels of Bt protein in their pollen. Secondly, the chemical composition of pollen can vary between different corn hybrids. Hence, toxicological studies must be done on the same corn hybrid that differs only by the presence of absence Bt. Otherwise, it is impossible to determine if any difference is due to a difference in chemical composition, or to the presence of a Bt protein. Finally, the dose makes the poison—a greater response to increasing amounts of a compound is considered to be the hallmark that something is really causing harm. Thus, if Bt proteins were really harming caddisflies, caddisflies fed greater amounts of Bt pollen should suffer more than those fed smaller amounts. Such a relationship was not observed. Importantly, harmful effects could not be detected when the study in the report was repeated in a stream rather than in a laboratory.

So far there is no hard evidence that Bt pollen can harm aquatic ecosystems. But, Bt can enter streams in other ways. It is naturally found in soils. Also, bits and pieces of Bt corn plants can get washed in to streams. Therefore, the topic continues to be studied to determine if harmful effects can be detected.