NOTE: A study (abstract below) on the water flea daphnia magna shows that GM Bt maize was toxic to this nontarget organism, compared with the non-GM isogenic (having the same genetic background) variety.

The GM-fed daphnia had higher mortality than the non-GM-fed daphnia. a lower proportion of females reached sexual maturation, and the overall egg production was lower compared to D. magna fed non-GM maize.

The study shows that the GM maize and the non-GM isogenic variety are not substantially equivalent to, or as safe as, one another. Nor can they be considered to have the same food value. Yet regulatory approvals of this and all other GM crops wrongly assume just the opposite.

The study also shows that Bt crops are not only toxic to target pests but also to other nontarget insects. Daphnia magna are a widely accepted ecotoxicology model - in other words, they are an indicator of environmental toxicity.

The particular GM maize tested stands accused of causing allergic and immune reactions in Philippine farmers:

This study is not new but we are reminding people about it since there seems to be renewed interest in it.
Bohn, T., et al. (2008). "Reduced fitness of Daphnia magna fed a Bt-transgenic maize variety." Arch Environ Contam Toxicol 55(4): 584-592.
Full paper available here:

Genetically modified (GM) maize expressing the Bt-toxin Cry1Ab (Bt-maize) was tested for effects on survival, growth, and reproduction of the water flea Daphnia magna, a crustacean arthropod commonly used as a model organism in ecotoxicological studies. In three repeated experiments, D. magna were fed 100% ground maize in suspension, using either GM or isogenic unmodified (UM) maize.

D. magna fed GM-maize showed a significantly reduced fitness performance: The mortality was higher, a lower proportion of females reached sexual maturation, and the overall egg production was lower compared to D. magna fed UM isogenic maize. We conclude that the tested variety of Bt-maize and its UM counterpart do not have the same quality as food sources for this widely used model organism. The combination of a reduced fitness performance combined with earlier onset of reproduction of D. magna fed Bt-maize indicates a toxic effect rather than a lower nutritional value of the GM-maize.

[Extract from conclusion]
In conclusion, our study demonstrated significant and negative long-term effects after feeding a transgenic Bt-maize variety. The combination of life-history traits indicates a toxic response of D. magna to the GM-maize.

Within our test system, we reject the null hypothesis that the tested GM-maize and UM-maize had the same quality as a food source. The observed effects of transgenic Bt-maize on D. magna call for greater attention, not only on the runoff material from transgenic agricultural fields but also on the sensitivity of aquatic nontarget organisms to transgenic products.