Ecotoxicology exam biol3203
Physiological responses to pollutants

Respiration

Cardiovascular

Oxidative metabolism (swimming)

Osmotic and ionic regulation

Feeding & Nutrition

Reproduction

Neurological

Behavioural.

Respiration

Can be Measured by O2 consumption or CO2 production.

Respiratory stress caused by Cu is worse in Cypridae than Onchorhyncus mykiss. It is not related to tissue damage but to disruption in ionoregulation. (DeBoeck 2006)

Cardiovascular

Heart rate BPM.

Cu increases HR in crabs (Brown 2004)

But this does not measure the stroke volume so circulation may not increase, could be as a clearance measure (Spicer 2007)

Oxidative metabolism and swimming

 

Ucrit is a measure of swimming speed.

Environmental ammonia reduced the swimming speed of Onchorhyncus mykiss (Wicks 2002)

Osmotic & Ionic regulation

Ion uptake rate.

Low pH and Al reduce the sodium uptake in pike fry. (Keinanen 2000) Could be because of denaturing channel and ion exchange proteins.

Feeding and Nutrition

Vitamin profiles, feeding rates, foraging success. Can be affected by a broad range of contaminants. Ammonia reduces feeding in Onchorhyncus mykiss(Wicks & Randal 2002)

Silver nanoparticles effect gut microbiota (Merrifield 2013)

PCB effect vit A&E profiles in Delphinapterus leucas (DeForges 2013)

Reproduction

Survival of offspring, No. produced, condition of organs.

Correlation between PCB/DDT concentration and the occurrence of lesions on ovaries in Delphinapterus leucas (Beland 1993).

Oestrogenic compounds can cause intersex in fish.

TBT imposex in Nucella lapulis

Neurological and Behaviour

Lipid soluble compounds can enter neurones via the myelin sheath and may be able to cross the blood brain barrier.

Mercury causes neurone degeneration which can affect behaviours and may be linked to mass strandings of cetacea. Prevents GTP from binding to tubulin. Blocks calcium channels preventing synaptic transfer of action potential. 

Environmental protection

Toxicity equivalents. Limits of tolerance. Development of biomarkers. Risk assessment. Pronlem formulation, risk analysis and characterisation.

Where do end points fit in. Which approaches and why.

Dose response relationship

Toxicity is relative: dose and properties determine whether a negative effect is observed.

Environment has a role to play, i.e. availability.

Dose is the amount of substance per body weight or liquid concentration.

Dose response parameter
Can be for one dose at differnt times or set time with different concentrations.
Toxicity
Exposure time and dose
Molecular basis

Toxins effect specific receptor sites.

Dose response is maximal when all receptors are bound to or no more disruption can occur.

Changes in the conformation of enzymes.

Effexts in the nervous system.

 

Dose response assumptions

Response proportional to concentration at target site.

Concentration at target site is related to dose.

The response is causally related to the compound investigated.

DISCUSS THESE HARD!?

End points of dose response

LOAEL
NOAEL
LC50

LD50

Pharmacological use of dose response

Therapeutic index = LD50/ED50 

Seperate the lethal and positive effects.

LC50

Lethal concentratio responsible for 50% of the deaths.

Is responsible for most of the deaths but some organisms will be sensitive/resistant.

Response measured.

Question dependent/

Quantal: death, presence/absence of lesions, behaviours.

Graded: Biochemical change, change in growth rate.

Threshold effects.

Threshold dose: no effect is measurable,

Concentration at which the response is not observed. NOAEL

Not observed in carcinogens.

Limited by curve fitting ability and graph making. Number of data points has an effect.

Safety factors

NOAEL x 10, 100, 1,000 etc.

e.g Acceptable daily intake = NOAEL mg kg-1d-1/100

WQS = NOAEL/1,000

Limitations

NOAEL not always present.

Data analysis- curve fitting, number of data.

With NOAEL: decide on acceptable level above background.

NOAEL doesn’t mean safe and long term exposure is much harder to test for. 

Often ethical and practical considerations prevent investigation of higher organisms.

Benefits

Universally accepted techniques give replicable results.

Gives information about which chemicals are most damaging to organisms inn general.

Biomarkers
Biological response to chemicals or radiation that gives a measure of exposure at cellular, tissue, organ, individual or population level (Peakall 1994).
Biomonitoring
Frequent or continula gathering of information from a given population that is relevant to that populations health risk.
Types of Biomarker
histological, biochemical, physiological, genetic, behavioural.
Chronic multiple exposure
Long term exposure to multiple contaminants at low levels mean that it is difficult to attribute changes to specific contaminants
Natural cycles
Natural cycles within organisms may be responsible for any number of physiological changes. E.g Crassostrea gigas haemocytes are governed by the seasons as well as gametogenesis, and other environmental stressors. (Duchemin 2007)
Multiparametric approach
Using information from a multitude of biomarkers (give examples) some researchers have attempted to create mathematical models for prediction of pollution gradients. These have mixed success with the largest obstacle being environmental factors and determination of reference sites,(Auffret 2006)
Background research

need to have an understanding of how the organism works and what chemicals do to it.

This can lead to the use of inappropriate sentinel organisms. For example mytilus are well studied and used in ecotoxicological experiments due to their economic importance. However there are molluscs that have increased sensitivity to pollutants that would be more suitable but are not used e.g Cerrastoderma edule (Giron-Perez 2009)

Routes of entry
Need to be fully understood. No use using an organism as a biomarker for a pollutant if it is completely insensitive or impermeable to that contaminant.
Standardised protocols
Expensive and lengthy investigations to develop best protocols. Need to be agreed upon. Differences between sexes need to be accounted for.
Cryptic stage
Use the most sensitive stage of the organism to indicate what the worst impast are
Trophic level in biomarkers

HIgher levels will show more damage from persistent bioaccumulated chemicals. Lower are more easily used- ethical issues, abundance, husbandry.

Some organisms employ different feeding strategies within species. For example orca can be divided into marine mammal feeders and piscivores. If antioxidant activity in blubber samples was used for a biomarker indicating mercury poisoning than the higher trophic level marine mammal eaters would be more likely to display an effect so it would be necessary to distinguish between the two subspecies.

Migrating animals
Problematic due to range of exposure as they travel through different environments. Can still be used where biological effect is short term such as HSPs but not for something like organ damage.
Normal levels
Difficult to determine for gene expression and enzyme activity but not for histopathology, though this requires euthanasia of organisms.
Laboratory test species
Well studied and understood. Genome known, sensitivities known but not suitable for in situ studies.
Biomonitoring VS Chemical assay
Less specific but more directly linked to ecosystem health. Can detect impacts of combined contaminants. Cannot id contaminants
Sentinels
Demonstrate presence of bioavailable contaminants and extent of exposure
Surrogates
Indicate potential human effects
Predictors
long term effect on ecosystem
Moore et al 2004
Neutral red dye retention assay used in black sea molluscs to determine stability of lysosome. Low times indicate membrane damage but not which chemical caused it.
Routes of Entry Intro
Across body surface, through GEO, through GIT
Integument of aquatic organisms
Fish: epidermis, dermis (scales), hypodermis.
Crustacea: cuticle, exoskeleton, moult cycle.
Soft bodied inverts: Epidermal layer.
Integument compounds
LMW, lipophilic
Fish skin
Thinner and more permeable then mammals. Maybe be very thin layer to the systemic circulation. Mucosal layer presents no barrier to diffusion of ions (Shephard 1981)
Skin consequences
Depends on: frequency of exposure & effects on blood flow and distribution
Plasma concentration
influence blood:tissue equilibrium
Small molecules
Utilise pores in capillaries. May Dissolve in the lipid membrane
Hg2+ Mercury
Can diffuse through calcium or sodium ion channels. May also diffuse across the cell membrane at physiological pH
Metal poisoning
Induction of metal chaperones and ; oxidative stress. Cu is particularly bad.
Through the skin
local damage of muscles-point of entry. Depends upon point or diffuse source from the environment.
Gastro intestinal tract (GIT). GUT
Broadest range of contaminant exposure and absorption.
Food
Contaminants that bioaccumulate on or within food items.
Feeding
Ingest contaminants in sediment and water that is eaten.
Gut microbiota
Bioactivation of compounds by bacteria. Make compounds bioavailable and/or more toxic. Also negatively impacted by contaminants e.g. silver nanoparticles (Merrifield et al 2013), which alter the community composition as they are toxic to some,potentially beneficial, of the gut microbiome.
Vetenary products
In the runoff from land (faecal and aquaculture waste).
Differences in species
Anatomical and feeding behavioural. Tilapia stir up sediment while feeding and zebra fish feed in the water column, differences in Hg concentration in the fish tissue.
Water chemistry differences
As salinity increases Cd uptake in Fundulus heteroclitus decreases as determined by radioisotope measurements of concentration in tissue. Also found that Cd decreases in gills and head but increases in the viscera indicating that increase in drinking for osmoregulation is maintaing some Cd (Dutton ; Fisher 2011).
Absorption

Lipid soluble-Throughout GIT.

Weak acids-Stomach.

Weak bases and acids-Small intestine.

Strong asids/alkali-Carrier mediated throughout.

Phagocytosi e.g botulinum

pH

Affects uptake. Oesophagus-Neutral

Stomach-pH 2

Anterior intestine-pH 6

GIT Consequences

Lipophilic compounds in fatty tissues.

Metals to the gills, liver and kidney.

Mostly non polar molecules affect the brain.

Expression of chaperones.

Biliary excretion.

Biliary excretion

Contaminants sequestered in bile then reabsorbed via the biliary duct and hepatic portal vein.

Toxic metabolites returned to the gut.

Increases hepatic exposure.

Saturated bile can cause liver necrosis.

Increases the half life of contaminants.

Route of entry: Gill
G.E.O. with large SA/V ratio. Short diffusion distance and excellent blood supply, only a few layers of cell between environment and circulatory system.
Mucous cells
Offer some protection but reduce efficiency of the gills exchange processes.
Contaminants cross the gill
Lipophilics, metals and small molecular weight organics.
Consequences of gill.

Damage to gill secondary lamellae e.g. hyperplasia caused by irritation.

Rapid distribution thoughout body.

Reduced excretion and gas exchange capability.

 

Distribution through circulation

Some contaminants such as copper can bind to plasma proteins, in Cu case albumin.

These restrict distribution to organs but enhance uptake to blood by lowering the plasma concentration.

Saturation of the blood may be the toxic threshold.

Endocrine system
System of glands producing hormones that are distributed throughout the body to taget systems using the circulatory system for transport. Glands: Hypothalamus: Pituitary: Pineal: Adrenal: Gonadal: Thyroid: Parathyroid: Pancreas: GIT.
Endocrine disruption
Occurs when an exogenous substance intereacts with any element of the endocrine system causing change in function.
Hormones
Peptides, Steroids or Amines.
Steroids
Made from lipids such as cholesterol, most sensitive to anthropogenic chemicals. Produced mainly in the gonads.
Main steroids
Testosterone, Estradiol and Glucocorticoids.
Steroid modes of action

Genomic: Steroid binds to receptor and translocates across cell membrane then diffuses into nuclear membrane and directly effects gene expression.

Non genomic: Steroid binds to receptor on cell surface and initiates autophosphorylation such as cAMP, producing an effect such as membrane bound ion channel modulation (Steinman ; Trainor 2007).

Target cell disruption
Blockers and mimics. Blockers prevent steroid binding. Mimics bind and cause an insufficient or excessive response that is generally inappropriately timed.
Hormone sensitization

Jansen 2004

Increase expression of hormone receptors by inhibitting the action of histone deacetylase which would otherwise reduce expression.

 

Biomarkers
Endocrine disrupting effects have been well studied in some species. For example tributyltin TBT causes imposex in the dog whelk (Nucella lapulis) (Smith 2006). In females a penis developed to block the oviduct eventually leading to sterility.
Mallard duck shells
Exposure to DDT causes a reduction in shell mass. This is likely caused by the 65% in Ca-ATPase activity. (Kolaja 1977)
Thyroid hormones.
Critical for growth and development particularly brain and nerone development.
Thyroid disruption in Orca
Villanger et al 2011 recorded that the blubber concentration of PCB PBDE and HCB were inversely correlated to thyroid hormone levels.

Alligator example

DDT DDE DDD

Metabolite of DDT apear to have caused changes in the levels of sex hormones in alligators in lake apopka.

 

Alligator effects
Reproductive issues. Hormone imbalance. Low hatching rates, physical abnormalities e.g. multiple eggs in one folicle. Genitals not producing properly. Increased estrogen to testosterone ratios in both sexes. ( DDT metabolites interacting with sex organs during development (Harrison 1999).
Crassostrea gigas fisheries in france.
TBT an antifoulant caused massive reductions in spatfall. This suggests that TBT was acting on the settling mechanism. Shell deformities in adults could be due to calcium metabolism being altered. (Rulz 1999)
Intersex in roach
Endogenous estrogen immitation by exogenous compound. Males with developing eggs. Vitellogenin synthesis initiated in liver. This is precursor to egg yolk. Caused by estrogen contamination from sewage (contraceptives)(Larsson 1999).
Dioxins and vitellogenin induction
Dioxins stop vitellogenin production. They cause AHR to form a complex with a nuclear translator and disrupt the estrogen receptor ? (ER?) autoregulatory transcriptional loop (Bemanian 2004).
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