RESUMO
Unconventional oil and natural gas (UOG) operations have emerged over the last four decades to transform oil and gas production in the United States and globally by unlocking previously inaccessible hydrocarbon deposits. UOG development utilizes many compounds associated with conventional oil and gas, as well as some specific to UOG extraction, particularly during hydraulic fracturing (HF). While research is increasing on UOG chemicals and their mixtures, this review discusses the current evidence for reproductive toxicity following exposures to UOG/HF mixtures. These complex chemical mixtures have been demonstrated to interact with numerous mechanisms known to influence reproductive health. A growing number of environmental and controlled laboratory testing studies have reported adverse reproductive health effects in animals exposed to various UOG chemical mixtures. An expanding body of epidemiological literature has assessed adverse birth outcomes, although none has directly examined reproductive measures such as time to pregnancy, semen quality, and other direct measures of fertility. The existing literature provides moderate evidence for decreased birth weights, increased risk of small for gestational age and/or preterm birth, increased congenital abnormalities, and increased infant mortality, though importantly, studies are widely variable in methods used. Most studies utilized distance from UOG operations as an exposure proxy and did not measure actual chemical exposures experienced by those living near these operations. As such, while there is growing evidence for effects on births in these regions and good mechanistic evidence for reproductive toxicity, there is much research still needed to make firm conclusions about UOG development and reproductive health.
RESUMO
Crustaceans comprise an ecologically and morphologically diverse taxonomic group. They are typically considered resilient to many environmental perturbations found in marine and coastal environments, due to effective physiological regulation of ions and hemolymph pH, and a robust exoskeleton. Ocean acidification can affect the ability of marine calcifying organisms to build and maintain mineralized tissue and poses a threat for all marine calcifying taxa. Currently, there is no consensus on how ocean acidification will alter the ecologically relevant exoskeletal properties of crustaceans. Here, we present a systematic review and meta-analysis on the effects of ocean acidification on the crustacean exoskeleton, assessing both exoskeletal ion content (calcium and magnesium) and functional properties (biomechanical resistance and cuticle thickness). Our results suggest that the effect of ocean acidification on crustacean exoskeletal properties varies based upon seawater pCO2 and species identity, with significant levels of heterogeneity for all analyses. Calcium and magnesium content was significantly lower in animals held at pCO2 levels of 1500-1999 µatm as compared with those under ambient pCO2. At lower pCO2 levels, however, statistically significant relationships between changes in calcium and magnesium content within the same experiment were observed as follows: a negative relationship between calcium and magnesium content at pCO2 of 500-999 µatm and a positive relationship at 1000-1499 µatm. Exoskeleton biomechanics, such as resistance to deformation (microhardness) and shell strength, also significantly decreased under pCO2 regimes of 500-999 µatm and 1500-1999 µatm, indicating functional exoskeletal change coincident with decreases in calcification. Overall, these results suggest that the crustacean exoskeleton can be susceptible to ocean acidification at the biomechanical level, potentially predicated by changes in ion content, when exposed to high influxes of CO2. Future studies need to accommodate the high variability of crustacean responses to ocean acidification, and ecologically relevant ranges of pCO2 conditions, when designing experiments with conservation-level endpoints.