Higher levels of growth hormone also found in non-organic milk, suggesting use of the GM growth hormone rbGH
Here's an important study that found residues of currently used antibiotics and pesticides in the milk of conventionally raised (non-organic) cows but not in organic milk. Some antibiotics were found in conventional milk at levels exceeding federal safety limits.
The study also found higher levels of the growth hormone bGH in the conventional milk. This suggests (but does not prove) that the farmers were dosing their cows with the genetically engineered bovine growth hormone rbGH, which is banned in Canada and Europe but allowed in the US.
The authors state that to the best of their knowledge, their study "is the first to compare levels of pesticides in the US milk supply by production method (conventional v. organic). It is also the first in a decade to measure antibiotic and hormone levels and compare them by milk production type".
The study does not assess the health impact of human exposure to the contaminants found in milk.
Production-related contaminants (pesticides, antibiotics and hormones) in organic and conventionally produced milk samples sold in the USA
Jean A Welsh, Hayley Braun, Nicole Brown, Caroline Um, Karen Ehret, Janet Figueroa, and Dana Boyd Barr
Public Health Nutrition, 27 February 2019
https://www.cambridge.org/core/services/aop-cambridge-core/content/view/D1107FE30C778A73F5F601C5D3D6E572/S136898001900106Xa.pdf/productionrelated_contaminants_pesticides_antibiotics_and_hormones_in_organic_and_conventionally_produced_milk_samples_sold_in_the_usa.pdf (open access)
Objective: Consumption of cow’s milk, which is associated with diet and health benefits, has decreased in the USA. The simultaneous increase in demand for more costly organic milk suggests consumer concern about exposure to production- related contaminants may be contributing to this decline. We sought to determine if contaminant levels differ by the production method used.
Design: Half-gallon containers of organic and conventional milk (four each) were collected by volunteers in each of nine US regions and shipped on ice for analysis. Pesticide, antibiotic and hormone (bovine growth hormone (bGH), bGH- associated insulin-like growth factor 1 (IGF-1)) residues were measured using liquid or gas chromatography coupled to mass or tandem mass spectrometry. Levels were compared against established federal limits and by production method.
Setting: Laboratory analysis of retail milk samples.
Results: Current-use pesticides (5/15 tested) and antibiotics (5/13 tested) were detected in several conventional (26–60 %; n 35) but not in organic (n 34) samples. Among the conventional samples, residue levels exceeded federal limits for amoxicillin in one sample (3 %) and in multiple samples for sulfamethazine (37 %) and sulfathiazole (26 %). Median bGH and IGF-1 concentrations in conventional milk were 9·8 and 3·5 ng/ml, respectively, twenty and three times that in organic samples (P < 0·0001). Conclusions: Current-use antibiotics and pesticides were undetectable in organic but prevalent in conventionally produced milk samples, with multiple samples exceeding federal limits. Higher bGH and IGF-1 levels in conventional milk suggest the presence of synthetic growth hormone. Further research is needed to understand the impact of these differences, if any, on consumers.