Here are the replies we've received from the homework assignments. Thank you to everyone that participated-- Enjoy!
Exposure routes relevant humans include 1), oral (ingestion), 2) topical (skin exposure), and 3) respiratory (inhalation).
exposure routes: oral, dermal, and inhalation
I think my top three for cetaceans would be (a) absorption and (b) aspiration (I think these are difficult routes for exposure assessment but could be important particularly if their contribution is underestimated so I think they merit a bit more attention) and then (c) inhalation, again because of the complexity of the respiratory system and the major differences between marine mammal lung and diving physiology and oxygen management compared to terrestrial species. This is where extrapolation from laboratory animal models to marine mammals perhaps becomes particularly hazardous!
1. Route, oxygen exchange through the gills, Florida pompano a pelagic fish exposure to dispersed oil similar to that of the DWH incident.
2. Route, ingestion, Red drum a coastal fish exposed to oil contaminated food
3. Route, multiple (i.e. inhalation through gills, ingestion and absorption through the skin, southern flounder a benthic fish exposed to oiled-sediments
1) Inhalation
2) ingestion
3) Transplacental? Just throwing this one out there
For the humans I am studying, inhalation and dermal contact are the most important exposure routes.
a. Water borne absorption
b. Dietary exposure
c. Sediment exposure (not relevant for all species)
Surface oil, in the form of volatiles or as small droplets, can be inhaled or aspirated by surfacing cetaceans, and therefore delivered to lung tissues and the bloodstream.
Several dolphins in Barataria Bay have been observed feeding in sediments (“drilling”), and there have been previous opportunistic observation of sediments weathered ("crust” looking) on the water and bottom surfaces, with visible oil in the middle during dolphin
captures, is there ongoing exposure of dolphins feeding on sediments? While regularly observed, it is unclear how prevalent this feeding behavior is among individual dolphins?
Lab exposure in fish (including in my lab) have demonstrated transgenerational effects in fish born from exposed parents, even though their whole life cycle took place in clean water. We are also seeing immune changes comparable to those observed in Barataria
Bay dolphins in recently sampled dolphins born after the DWH spill. Are we seeing transgenerational health effects in dolphins?
1. Ingestion
2. Dermal
3. Inhalation
a. Inhalation
b. Dermal, ocular
c. Ingestion of contaminated seafood
1. Due to their propensity for burrow-dwelling and continual maintenance, tilefish are exposed to settled crude in the sediments by: dermal contact while within the burrows, ingestion of muds during burrow maintenance, and exposure to contaminants from mixed sediments entering the water column while the burrows are excavated.
2. During a GOMOSES session in 2017, several scientists noted that fish that eat crustaceans appeared to be more negatively impacted by PAH effects, based upon the talks presented. I’m not sure if this had been investigated further.
3. Given their high association with oil rigs and pipeline structure, it’s possible snapper are receive acute exposure to produced waters and point-source releases of oil products.
a. Dietary exposure to oil using etubes rather than gavage had both pros and cons for the method; pros-we knew the exact amount of oil ingested; cons-inflamation responses at the surgical site made any immune system responses to oil impossible to determine.
b. Evidence of oxidative stress in turtles exposed to oil; changes in antioxidant systems; induction of oxidative damage, including lipid peroxidation and DNA damage (as single strand breaks).
c. Some evidence for adrenal dysfunction in turtles as a result of oil exposure.
d. Species specific differences in response in the two freshwater surrogate species used.
e. Malabsorption and dehydration in turtles exposed to oil
f. Bile metabolites directly correlate well to the extent of oil ingestion
g. Estimated gut retention of oil is much higher than we observed in our studies i.e. 9 days versus <48 hours.
h. A two-week oil ingestion study only showed slight changes and mild effects; clinically within normal levels.
Knowledge gaps include a need for 1) biomarkers of exposure and effect, 2) baseline data, and 3) improved risk assessments and risk communication.
data gaps: baseline health, endocrine evaluations, and effects of inhalation on lung function.
I think the data gaps of interest relate to reproductive effects. There seems to be a lot of evidence for various effects from fertility and pregnancy to effects on the uterus and ovaries. How much is mediated through the AHR is critical and I found some interesting papers on bax-dependent apoptosis in developing fetal ovarian germ cells which would suggest transgenerational effects? So my three examples would all relate to reproduction – pregnancy – what is the mechanism for effects on for example gestational length? Fetal viability - How does resorption or spontaneous abortion in cetaceans particularly occur? And uterine and ovarian physiology - What is the effect on uterine physiology (particularly on 17beta-oestradiol signalling which has recently been shown to be impacted by 3-MC in mice?).
Maybe this is too much into the molecular biology (and my knowledge at that level is limited!) but I think if we can investigate the similarities between taxa at the cellular and biochemical levels then we might be able to better predict susceptibilities based on evolutionary differences or phylogenetic similarities etc.
1. Anthropogenic evolution, in which sustained exposure to contaminants of wild fish populations leads to phenotypic and genetic change caused by contaminant-induced selection pressure.
2. Sensitivity differences of oil/dispersed oil among different adult fish species (any relevant fish species) when exposed to low contaminant loads, what are the sublethal effects and which species most vulnerable.
3. Maternal transfer of lipophilic contaminants to female fish eggs (any relevant fish species).
1) Mechanisms of adrenal effects
2) How can we determine exposure levels in cetaceans during a spill including off-shore species.
3) Mechanisms/pathogenesis of Reproductive effects
4) How do indirect ecosystem perturbations during a spill (i.e. decreased fatty acids in fish during spill, general changes in habitat like increased vessel traffic or decreased sea grass/coral, benthic communities) affect the health of top of the food chain cetaceans
- Information on dispersed crude oil and its functional toxicity, compared with that for crude oil alone.
- Actual exposure assessment is always a problem in human populations. We have a questionnaire which attempted to get at what people were exposed to, however, understanding the mixtures of what they were exposed to and the timing of their exposures, it very challenging.
- Exposome data will be very useful to generate for these exposures, however, there is still very little data (very few studies which have focused on this) from metabolomics studies.
a. How sub-lethal effects manifest on organismal and population levels of performance. Note that this relates to true sub-lethal endpoints, not endpoints that describe a non-lethal effects that is almost certain to be lethal without external influence.
b. A more thorough examination of non-cardiac toxicity. There is growing evidence that cardiotoxicity is not the only story when it comes to oil toxicity in aquatic environments.
c. The mechanistic origin of non-cardiac impairments. Are these simply downstream consequences of cardiac impairment, or is there a mechanism that we are missing.
Lab exposure in fish (including in my lab) have demonstrated clear reproductive effects that could lead to decreased populations. Have such changes taken place in the northern Gulf Mexico, and could changes in the food chain have resulted in indirect effects
of ecosystem oil exposure on food availability and fitness in higher trophic levels such as dolphins? Could this have resulted in dolphin growth retardation? We have observed dolphins significantly older when aged via tooth X-ray than their length had suggested.
How consistent are oil toxicity effects across taxa, and how conserved are putative mechanisms of oil toxicity across taxa? How much do we know about specific mechanisms and what else would we need to know in order to assess how conserved mechanisms are? Are
dose-response relationships consistent across species? Are effects PAH-specific, and would such specificity be conserved across species?
How linked are effects across systems? For example, oil effects on stress response have the potential to affect the immune system, and immune system effects have the potential to affect pregnancy. Are mechanisms conserved between systems or mostly system-specific and independent between systems?
1. Effects on the hypothalamic pituitary adrenal (HPA) axis*
2. Dispersant effects
3. Inhalational / respiratory effects*
*Particularly any clinically-relevant effects
a. Timeliness or time concordance variation of exposure data
b. Collection of toxicologic exposure data
c. Assessment of indirect or situational exposure data
1. Does the rate of PAH metabolism and excretion vary between tilefish populations experiencing different levels of chronic exposure?
2. What are the mixed effects of multiple contaminant exposures on fish (metals, PAHs, PCBs, pesticides, sewage, etc)?
3. How much of an effect do annual fluctuations in Mississippi river discharge have on demersal species?
4. What are the differences in dietary bioaccumulation by prey items?
a. Is there an impact to the adrenal system in turtles following exposure to oil? A hint of requires longer term exposures and following post-exposure for delayed responses
b. How important is the inhalation route of exposure for turtles exposed to surface oil?
c. Which turtle species are the best surrogate species for sea turtles ? Would an estuarine turtle (e.g. diamondback terrapin) be better than a freshwater species ? (e.g. red-eared slider)
d. Is impact to the salt gland in turtles an important effect of oil exposure? How can this be studied if only freshwater surrogate turtle species are used?
e. Impact of physical oil/heat on turtles as they swim through surface oil slicks
f. Longer term implications of sublethal exposure to oil; tissue residues, maternal transfer to yolk and impact to offspring
g. Are hatchling turtles more sensitive to oil expsosure than juvenilles or adults?, what about developing embryos?
h. Does oil exposure alter the sex ratio in developing turtle embryos?
i. Need more data on electrolyte disturbance/imbalance in turtles exposed to oil; for example, potassium levels.
(1) I’d like to expand our understanding of the interactions between oil toxicity and disease(s), including susceptibility of exposed organisms to disease, susceptibility of health-compromised organisms to oil, interaction terms, etc.
(2) Neurotoxicity, including interference with AP’s, developmental effects, neurotransmitters, etc. I’m also really interested in exploring effects of oil on sensory functions: lateral line/neuroblast/hair cell; optical development and function; olfaction; interaction terms in organisms that might be multiply sensory compromised.
(3) Behavioral effect challenges, including potential HPA-mediated responses, possible linkages to neurotransmitter and sensory deficits.
(4) Expanded understanding of photo tox, e.g.; photo-modified products; maternal transfer (“Bam” testing); sublethal responses in environmentally relevant UV exposure regimes.