Fumonisin B1 toxicity in swine: a comparative analysis of genetically engineered Bt corn and non-Bt corn by using quantitative dietary exposure assessment modeling and ecotoxicological investigations on earthworms

Fumonisin B1 (FB1) is a ubiquitous mycotoxin produced by Fusarium verticilliodes and F. proliferatum, and is a common biological contaminant of corn (Zea mays L) and other grains. Currently the acute effects from FB1 exposures are well-documented and managed in the swine industry; however, practices to limit prolonged low-dose exposures to FB1 have been less fully considered and may negatively impact production efficiency. For decades research involving Fusarium and its associated mycotoxins has focused on human, animal and plant health. As result there is limited knowledge of ecological mycotoxicology, with the least understanding pertaining to invertebrate ecotoxicological hazard potential. Two separate quantitative dietary exposure assessment (QDEA) models were conducted to estimate the long-term exposure of FB1 in nursery and grower-finisher swine diets. Estimated concentrations of FB1 in swine diets were compared to associated toxicological adverse effects established from the literature. Both QDEA models used deterministic and partially stochastic parameters, which incorporated weekly dietary designs including genetically engineered Bacillus thuringiensis (Bt)-corn, conventional non-Bt corn, and distillers dried grains with solubles (DDGS). Six feeding scenarios differing in the source of corn in diets were modeled to assess variation in FB1 exposure representing a mixture of (1) Bt and non-Bt grain and DDGS (blended); (2) Bt grain and Bt DDGS; (3) non-Bt grain and non-Bt DDGS; (4) Bt and non-Bt grain; (5) Bt grain; and (6) non-Bt grain. Nursery phase QDEA long-term exposure estimates (49 d duration) were compared to chronic levels of concern (LOC) found in the literature. The initial level of concern (LOC1; 1 mg FB1/kg diet), represents the lowest observed adverse effects concentration resulting in a decrease of average daily gain in nursery swine. Concentrations of 5 mg FB1/kg diet represent the second level of concern (LOC2), where pulmonary pathological alterations and a significant dose-dependent increase in pulmonary weight may occur in nursery swine. Exposure estimates indicated LOC1 was frequently exceeded regardless of feeding scenario, however; LOC2 was not reached. Diets where the corn fraction was entirely from Bt-corn showed the lowest FB1 exposure (exceeding LOC1 in 35% of occasions), while either a blended diet or diets using non-Bt grain and DDGS sources more commonly exceeded this threshold (95% of occasions). Based on these estimates, under blended corn source feeding conditions, swine populations in nursery facilities may frequently exhibit incipient effects (i.e., LOC1) of FB1 toxicity; however, impacts on production efficiency remain uncertain. Grower-finisher QDEA long-term exposure estimates (20 weeks) were compared to the chronic toxicological incipient LOC (1.0 mg of FB1/kg of diet). Results from both deterministic and semi-stochastic models demonstrated a distinct difference of FB1 toxicity in feed between Bt corn and non-Bt corn. Semi-stochastic results predicted the lowest FB1 exposure for Bt grain with a mean of 1.5 mg FB1/kg diet and the highest FB1 exposure for a diet consisting of non-Bt grain and non-Bt DDGS with a mean of 7.87 mg FB1/kg diet. Results from the deterministic synthesis closely mirrored but tended to slightly under-predict the mean result for the semi-stochastic analysis. This novel comparative QDEA model reveals that diet scenarios where the source of grain is derived from Bt corn presents less potential to induce FB1 toxicity than diets containing non-Bt corn. Fumonisins may have the potential for environmental cycling from swine manure agronomic applications and be potentiated further by conservation tillage practices. To assess the ecotoxicological hazard potential of FB1 on terrestrial invertebrates, an acute 14 day microcosm study was conducted under controlled laboratory conditions exposing the earthworm species Eisenia fetida to FB1 in an artificial soil (AS) system. Exposure concentrations were 1, 3 and 6 fold greater than the estimated environmental concentration (EEC): 2 mg FB1/kg AS, 6 mg FB1/kg AS and 12 mg FB1/kg AS, respectively. Fumonisin B1 was treated onto alfalfa meal, which was used as the food source. E. fetida survival and growth were measured in each treatment. E. fetida survival was 100% in all treatments. Results revealed a mean individual percent body weight increase from day 1 to day 14 for the negative control and all FB1 treatments: 24% (negative control), 34% (1xEEC), 35% (3xEEC) and 30% (6xEEC). Relative to the negative control, treatment 1 increased mean individual percent body weight by 9%, treatment 2 by 10% and treatment 3 by 5%. Mean individual percent body weight declined by 45% for the positive control (500 mg pendimethalin/kg AS). Considering the conservative dosimetry exceeding the EEC by a maximum of six fold, it is concluded that acute environmental exposures of FB1 presents minimal ecotoxicological hazard potential to E. fetida