Editing Bacillus thuringiensis (section)

===Safety studies===
The use of Bt [[toxin]]s as [[Insecticide#Plant-incorporated protectants|plant-incorporated protectants]] prompted the need for extensive evaluation of their safety for use in foods and potential unintended impacts on the environment.<ref>{{Cite web|url=https://gmoscience.org/2015/08/10/is-bt-toxin-safe/|title=Are all forms of Bt toxin safe?|website=Gmoscience.org|access-date=9 April 2022}}</ref>

====Dietary risk assessment====
Concerns over the safety of consumption of genetically modified plant materials that contain [[Delta endotoxin|Cry proteins]] have been addressed in extensive dietary risk assessment studies. As a toxic mechanism, ''cry'' proteins bind to specific receptors on the membranes of mid-gut ([[epithelial]]) cells of the targeted pests, resulting in their rupture. While the target pests are exposed to the toxins primarily through leaf and stalk material, Cry proteins are also expressed in other parts of the plant, including trace amounts in maize kernels which are ultimately consumed by both humans and animals.<ref>{{cite journal | vauthors = Fearing PL, Brown D, Vlachos D, Meghji M, Privalle L | title = Quantitative analysis of CryIA (b) expression in Bt maize plants, tissues, and silage and stability of expression over successive generations. | journal = Molecular Breeding | date = June 1997 | volume = 3 | issue = 3 | pages = 169–176 | doi = 10.1023/A:1009611613475 | s2cid = 34209572 }}</ref> However, other organisms (including humans, other animals and non-targeted insects) that lack the appropriate receptors in their gut cannot be affected by the ''cry'' protein, and therefore are not affected by Bt.<ref name="auto"/><ref name="auto1"/>

=====Toxicology studies=====
Animal models have been used to assess human health risk from consumption of products containing Cry proteins. The United States Environmental Protection Agency recognizes mouse acute oral feeding studies where doses as high as 5,000&nbsp;mg/kg body weight resulted in [[No-observed-adverse-effect level|no observed adverse effects]].<ref>{{cite web|publisher=US EPA|date=2001|url=http://www3.epa.gov/pesticides/chem_search/reg_actions/pip/bt_brad2/2-id_health.pdf |archive-url=https://web.archive.org/web/20151211051629/http://www3.epa.gov/pesticides/chem_search/reg_actions/pip/bt_brad2/2-id_health.pdf |archive-date=2015-12-11 |url-status=live|title=Bt Plant-Incorporated Protectants October 15, 2001 Biopesticides Registration Action Document|access-date=2022-04-09}}</ref> Research on other known toxic proteins suggests that {{clarify|text=toxicity occurs at much lower doses|reason=This statement is likely the opposite of what was intended.|date=November 2020}}, further suggesting that Bt toxins are not toxic to mammals.<ref>{{cite journal | vauthors = Sjoblad RD, McClintock JT, Engler R | title = Toxicological considerations for protein components of biological pesticide products | journal = Regulatory Toxicology and Pharmacology | volume = 15 | issue = 1 | pages = 3–9 | date = February 1992 | pmid = 1553409 | doi = 10.1016/0273-2300(92)90078-n | url = https://zenodo.org/record/1258447 }}</ref> The results of toxicology studies are further strengthened by the lack of observed toxicity from decades of use of ''B. thuringiensis'' and its crystalline proteins as an insecticidal spray.<ref>{{cite journal | vauthors = Koch MS, Ward JM, Levine SL, Baum JA, Vicini JL, Hammond BG | title = The food and environmental safety of Bt crops | journal = Frontiers in Plant Science | volume = 6 | pages = 283 | date = April 2015 | pmid = 25972882 | pmc = 4413729 | doi = 10.3389/fpls.2015.00283 | doi-access = free }}</ref>

=====Allergenicity studies=====
Introduction of a new protein raised concerns regarding the potential for allergic responses in sensitive individuals. [[Bioinformatics|Bioinformatic]] analysis of known [[allergen]]s has indicated there is no concern of [[Allergy|allergic reactions]] as a result of consumption of Bt toxins.<ref>{{cite journal | vauthors = Randhawa GJ, Singh M, Grover M | title = Bioinformatic analysis for allergenicity assessment of Bacillus thuringiensis Cry proteins expressed in insect-resistant food crops | journal = Food and Chemical Toxicology | volume = 49 | issue = 2 | pages = 356–62 | date = February 2011 | pmid = 21078358 | doi = 10.1016/j.fct.2010.11.008 }}</ref> Additionally, [[Allergy#Skin prick testing|skin prick testing]] using purified Bt protein resulted in no detectable production of toxin-specific [[Immunoglobulin E|IgE]] antibodies, even in [[Atopy|atopic]] patients.<ref>{{cite journal | vauthors = Batista R, Nunes B, Carmo M, Cardoso C, José HS, de Almeida AB, Manique A, Bento L, Ricardo CP, Oliveira MM | title = Lack of detectable allergenicity of transgenic maize and soya samples | journal = The Journal of Allergy and Clinical Immunology | volume = 116 | issue = 2 | pages = 403–10 | date = August 2005 | pmid = 16083797 | doi = 10.1016/j.jaci.2005.04.014 | url = http://repositorio.insa.pt/bitstream/10400.18/114/1/Lack%20of%20detectable%20allergenicity.pdf | hdl = 10400.18/114 }}</ref>

=====Digestibility studies=====
Studies have been conducted to evaluate the fate of Bt toxins that are ingested in foods. Bt toxin proteins have been shown to digest within minutes of exposure to simulated [[Gastric acid|gastric fluids]].<ref>{{cite journal | vauthors = Betz FS, Hammond BG, Fuchs RL | title = Safety and advantages of Bacillus thuringiensis-protected plants to control insect pests | journal = Regulatory Toxicology and Pharmacology | volume = 32 | issue = 2 | pages = 156–73 | date = October 2000 | pmid = 11067772 | doi = 10.1006/rtph.2000.1426 }}</ref> The instability of the proteins in digestive fluids is an additional indication that Cry proteins are unlikely to be allergenic, since most known food allergens resist degradation and are ultimately [[Small intestine#Absorption|absorbed]] in the small intestine.<ref>{{cite journal | vauthors = Astwood JD, Leach JN, Fuchs RL | title = Stability of food allergens to digestion in vitro | journal = Nature Biotechnology | volume = 14 | issue = 10 | pages = 1269–73 | date = October 1996 | pmid = 9631091 | doi = 10.1038/nbt1096-1269 | s2cid = 22780150 }}</ref>

=====Persistence in environment=====
Concerns over possible environmental impact from accumulation of Bt toxins from plant tissues, pollen dispersal, and direct secretion from roots have been investigated. Bt toxins may persist in soil for over 200 days, with [[half-life|half-lives]] between 1.6 and 22 days. Much of the toxin is initially degraded rapidly by microorganisms in the environment, while some is [[adsorbed]] by organic matter and persists longer.<ref name="Helassa">{{cite book | vauthors = Helassa N, Quiquampoix H, Staunton S | veditors = Xu J, Sparks D | title=Molecular Environmental Soil Science|date=2013|publisher=Springer Netherlands|isbn=978-94-007-4177-5|pages=49–77|chapter=Structure, Biological Activity and Environmental Fate of Insecticidal Bt (Bacillus thuringiensis) Cry Proteins of Bacterial and Genetically Modified Plant Origin| doi = 10.1007/978-94-007-4177-5_3 }}</ref> Some studies, in contrast, claim that the toxins do not persist in the soil.<ref name="Helassa" /><ref>{{cite journal | vauthors = Dubelman S, Ayden BR, Bader BM, Brown CR, Jiang, Vlachos D | year = 2005 | title = Cry1Ab Protein Does Not Persist in Soil After 3 Years of Sustained Bt Corn Use | journal = Environ. Entomol. | volume = 34 | issue = 4| pages = 915–921 | doi=10.1603/0046-225x-34.4.915| doi-access = free }}</ref><ref>{{cite journal | vauthors = Head G, Surber JB, Watson JA, Martin JW, Duan JJ | year = 2002 | title = No Detection of Cry1Ac Protein in Soil After Multiple Years of Transgenic Bt Cotton (Bollgard) Use | journal = Environ. Entomol. | volume = 31 | issue = 1| pages = 30–36 | doi=10.1603/0046-225x-31.1.30| doi-access = free }}</ref> Bt toxins are less likely to accumulate in bodies of water, but pollen shed or [[soil runoff]] may deposit them in an aquatic ecosystem. Fish species are not susceptible to Bt toxins if exposed.<ref>{{cite journal | vauthors = Clark BW, Phillips TA, Coats JR | title = Environmental fate and effects of Bacillus thuringiensis (Bt) proteins from transgenic crops: a review | journal = Journal of Agricultural and Food Chemistry | volume = 53 | issue = 12 | pages = 4643–53 | date = June 2005 | pmid = 15941295 | doi = 10.1021/jf040442k | hdl = 10161/6458 | url = http://dukespace.lib.duke.edu/dspace/bitstream/handle/10161/6458/Clark%20et%20al.%202005%20Bt%20Review.pdf?sequence=1 }}</ref>

=====Impact on non-target organisms=====
The toxic nature of Bt proteins has an adverse impact on many major crop pests, but some ecological risk assessments has been conducted to ensure safety of beneficial non-target organisms that may come into contact with the toxins. Toxicity for the monarch butterfly, has been shown to not reach dangerous levels.<ref>{{cite journal | vauthors = Sears MK, Hellmich RL, Stanley-Horn DE, Oberhauser KS, Pleasants JM, Mattila HR, Siegfried BD, Dively GP | title = Impact of Bt corn pollen on monarch butterfly populations: a risk assessment | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 98 | issue = 21 | pages = 11937–42 | date = October 2001 | pmid = 11559842 | pmc = 59819 | doi = 10.1073/pnas.211329998 | bibcode = 2001PNAS...9811937S | doi-access = free }}</ref> Most soil-dwelling organisms, potentially exposed to Bt toxins through root exudates, are probably not impacted by the growth of Bt crops.<ref>{{cite journal | vauthors = Saxena D, Stotzky G | year = 2000 | title = ''Bacillus thuringiensis'' (Bt) toxin released from root exudates and biomass of Bt corn has no apparent effect on earthworms, nematodes, protozoa, bacteria, and fungi in soil | url = http://www.ask-force.org/web/Bt/Saxena-Stotzky-2001.pdf | journal = Soil Biology & Biochemistry | volume = 33 | issue = 9| pages = 1225–1230 | doi=10.1016/s0038-0717(01)00027-x}}</ref>