In addition to illustrating the difficulty of predicting exposure pathways that may vary among landscape contexts, our study provides evidence that even trace levels of contaminants may impair reproductive success of free-living songbirds.
The difficulty of accurate exposure assessment is a major limitation in trying to understand potential associated health risks.
It is suggested that the use of biomarkers for persistent chemicals may be useful to mitigate the difficulty of determining exposure, while the use of more prevalent and timely end points, such as carcinogen-DNA adducts or oncogene proteins, may make the latency and rarity problems more tractable.
There are many reasons for this including, inter alia, the magnitude of the numbers of agents to be investigated, a shift away from occupational cancer research in the epidemiologic community and into new areas of epidemiologic interest, the difficulty and challenge of exposure assessment, and increasing barriers to accessing human subjects for occupational studies.
This illustrates the difficulties associated with assessment of exposure, pesticide exposure often being inferred from parental occupation rather than direct measurement.
Difficulties of managing asbestos exposures arising during industrial maintenance and repair and the problems of health protection of workers worldwide have been reported (Wagner, 2007).
These authors outline the difficulties of estimating REC exposures which began with the introduction of diesel engines into the mines in 1940s to 1960s.
The small difference in operation time is in contrast to other studies [ 14, 30, 31] with more technical difficulties in exposure of the proximal part of the tibia, altered anatomy and soft tissue imbalance.
Finally, a cross-sectional study design has several inherent weaknesses, such as lack of long-term observation for outcome and difficulty interpreting the association of exposure with outcome.
Adequately controlled studies of the effect of maternal HIV exposure on child health outcomes are rare, in part because of the difficulties of distinguishing between HIV exposure itself and socioeconomic factors associated with parental HIV infection.
