Bees could be the sentinels of rural environments but at least for these
authors "dogs may serve as sentinels for potentially harmful environmental
exposures in humans.

http://www.sciencedirect.com/science/article/pii/S0048969713003100
(only have access to abstract)

Abstract

Exposure to herbicide-treated lawns has been associated with significantly
higher bladder cancer risk in dogs. This work was performed to further
characterize lawn chemical exposures in dogs, and to determine
environmental factors associated with chemical residence time on grass. In
addition to concern for canine health, a strong justification for the work
was that dogs may serve as sentinels for potentially harmful environmental
exposures in humans. Experimentally, herbicides [2,4-dichlorophenoxyacetic
acid (2,4-D), 4-chloro-2-methylphenoxypropionic acid (MCPP), dicamba] were
applied to grass plots under different conditions (e.g., green, dry brown,
wet, and recently mowed grass). Chemicals in dislodgeable residues were
measured by LC-MS at 0.17, 1, 24, 48, 72 h post treatment. In a separate
study, 2,4-D, MCPP, and dithiopyr concentrations were measured in the urine
of dogs and in dislodgeable grass residues in households that applied or
did not apply chemicals in the preceding 48 h. Chemicals were measured at
0, 24, and 48 h post application in treated households and at time 0 in
untreated control households. Residence times of 2,4-D, MCPP, and dicamba
were significantly prolonged (P < 0.05) on dry brown grass compared to
green grass. Chemicals were detected in the urine of dogs in 14 of 25
households before lawn treatment, in 19 of 25 households after lawn
treatment, and in 4 of 8 untreated households. Chemicals were commonly
detected in grass residues from treated lawns, and from untreated lawns
suggesting chemical drift from nearby treated areas. Thus dogs could be
exposed to chemicals through contact with their own lawn (treated or
contaminated through drift) or through contact with other grassy areas if
they travel. The length of time to restrict a dog's access to treated lawns
following treatment remains to be defined. Further study is indicated to
assess the risks of herbicide exposure in humans and dogs.

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