Chemical (and other) stress in DEB 1: Introduction Tjalling Jager Dept. Theoretical Biology

Lectures on (eco)toxicity 1.Introduction toxic stress is important (and interesting) logical link to DEB theory brief history of toxic stress in DEB 2.Toxicokinetics uptake and elimination of chemicals in the body 3.Toxicodynamics and survival target sites and affected parameters effects on survival 4.Sub-lethal effects case studies, effects on growth and reproduction 5.Extrapolation e.g., population effects, time-varying exposure

Which chemicals are toxic? All of them! Paracelsus ( ): “The dose makes the poison” So toxicity is everywhere!

Natural toxicants: elements Metals e.g., iron, zinc, cadmium human use: Cd in pigment, stabiliser in plastics, batteries, electroplating natural occurence: zinc and phosphate ores

Natural toxicants: byproducts Polycyclic Aromatic Hydrocarbons (PAHs) e.g., phenanthrene, fluoranthene, benzo[a]pyrene human: cigarette smoke, cooking, combustion of fuel natural: in oil, coal, and tar deposits, forest fires

Natural toxicants: byproducts Dioxins e.g., 2,3,7,8-TCDD human: paper and fiber bleaching, incineration of waste, metal smelting, cigarette smoke natural: incomplete combustion of chlorine-containing things

Natural toxicants: defense Oleandrin oleander (Nerium oleander) gastrointestinal and cardiac effects, skin irritation, CNS effects (coma), death

Natural toxicants: defense Pyrethrin pyrethrum (Chrysanthemum cinerariaefolium) neurotoxic and repellent for insects

Natural toxicants: defense Alkaloids 10-25% of higher plants, ladybirds, poison dart frogs, cinnabar moth,... bitter taste, range of metabolic effects, recreational drugs...

Natural toxicants: competition Juglone black walnut (Juglans nigra) respiratory inhibitor for many plant species

Natural toxicants: offense “Venom” spiders, snakes, cone snails, jellyfish...

Natural toxicants: utility Nonylphenol velvet worm (Euperipatoides kanangrensis) squirts slime that contains nonylphenol  surfactant that is toxic, endocrine disruptor  production and use by humans restricted in EU

Natural toxicants: bacteria Botulinum toxin botulism (Clostridium botulinum) powerful neurotoxin (“most toxic compound known”), for cosmetic treatment “botox”

Natural toxicants: infochemicals  Prey respond to chemical cues from predators life history, morphological, behavioural changes e.g., helmet and spine in Daphnia lumholtzi e.g., mice fear the smell of cats

To summarise …  Toxicity is inherent to life all chemicals are toxic (even nutrients) many species evolved chemicals intended to be toxic all species evolved mechanisms to deal with excess nutrients and unwanted chemicals concentration too muchoktoo little performance

To summarise …  Toxicity is inherent to life all chemicals are toxic (even nutrients) many species evolved chemicals intended to be toxic all species evolved mechanisms to deal with excess nutrients and unwanted chemicals concentration too muchok performance

Human-made toxicants  Wide variety of uses paints, detergents, solvents, pesticides, pharmaceuticals, polymers, … probably some compounds  Chemical industry is BIG business! production value 2009: 3.4 trillion dollar ( $) equals the GDP of Germany  All are toxic, some are intended to kill fungicides, insecticides, herbicides, nematicides, molluscicides, …

Pesticides in agriculture  In the Netherlands in 2008: 5.6 million kg a.i. average 6.9 kg a.i./ha worst crop: lily bulbs at 99 kg a.i./ha

Human-made vs. natural What is the difference?  Time scale major increase after second world war rapid development of new types of molecules  Spatial scale amounts emitted landscape and even global instead of local  Since 1970’s, most countries have programmes for environmental protection...

In 1962 …

Ecotoxicology  Studies the effect of chemical stress from molecular level to ecosystems  But, in practice focus on man-made chemicals … not birds and mammals … individual level effects... environmental risk assessment... standardised experimental tests  For example the Daphnia reproduction test OECD guideline 211

Reproduction test

wait for 21 days …

Range of Concentrations

Dose-response plot EC50 total offspring log concentration NOEC

If EC50 is the answer … … what was the question? “What is the concentration of chemical X that leads to 50% effect on the total number of offspring of Daphnia magna (Straus) after 21-day constant exposure under standardised laboratory conditions?”  What does this answer tell me about other situations? (almost) nothing!

Organisms are complex

Stressing organisms … only adds to the complexity  Response to stress depends on organism (species, life stage, sex, …) endpoint (size, reproduction, development, …) type of stressor (toxicant, radiation, parasites, …) exposure scenario (pulsed, multiple stress, …) environmental conditions (temperature, food, …) etc., etc.

Complexity Environmental chemistry … predict the concentrations of chemicals in the environment from emissions and physico-chemical properties

Idealisation  E.g., multimedia-fate or “box” models mechanistic, mass balance, area:volume

external concentration (in time) toxico-kinetic model toxico-kinetic model TKTD modelling internal concentration in time process model for the organism process model for the organism effects on endpoints in time toxicokinetics toxicodynamics

Simplifying biology? At the level of the individual …  how much biological detail do we minimally need … to explain how organisms grow, develop and reproduce to explain effects of stressors on life history to predict effects for untested situations without being species- or stressor-specific

Simplifying biology? At the level of the individual …  how much biological detail do we minimally need … to explain how organisms grow, develop and reproduce to explain effects of stressors on life history to predict effects for untested situations without being species- or stressor-specific  Forget the details and focus on energy budget! how is food used to fuel the life cycle?

E.g., effect on reproduction

To understand an effect on reproduction … need to know how food is used to make offspring and how chemicals interfere with this process

eggs mobilisation Standard DEB animal structure somatic maintenance  growth maturity maintenance 1-  reproduction maturity buffer maturation p foodfeces assimilation reserve b

Different food densities Jager et al (2005)Zimmer et al (in prep.)

other stressors? structure foodfeces maturity maintenancesomatic maintenance assimilation  1-  growth reproduction maturity buffer maturation b p reserve mobilisation eggs ?

Stressor effects in DEB external concentration (in time) toxico- kinetics toxico- kinetics internal concentration in time DEB parameters in time DEB model DEB model repro growth survival feeding hatching … food stress parasites, ageing

Stressor effects in DEB external concentration (in time) toxico- kinetics toxico- kinetics internal concentration in time DEB parameters in time DEB model DEB model Internal concentration are often not measured … repro growth survival feeding hatching … DEB parameter cannot be measured …

A brief history of ‘DEBtox’ Corresponds with origin of DEB in 1979 egg

A brief history of ‘DEBtox’ The 80’s …  Kooijman (1981) toxicokinetics determines survival pattern  Kooijman & Metz (1984) toxicants affect energy budgets and thereby population response egg

A brief history of ‘DEBtox’ egg The early 90’s …  Parallel to OECD trajectory review test guidelines with respect to statistical analysis 1996: “analyse time course of effects” and “prefer mechanistic models”

A brief history of ‘DEBtox’ Birth in 1996 …  Windows software and booklet (Kooijman & Bedaux, 1996)  Series of papers Bedaux & Kooijman (1994) Kooijman & Bedaux (1996) Kooijman et al (1996)

A brief history of ‘DEBtox’ And 10 years later …  ISO/OECD (2006) DEBtox next to methods for NOEC and EC50  ECB workshop (2007) presenting DEBtox to EU risk assessors

eggs mobilisation ‘DEBtox’ simplification structure somatic maintenance  growth maturity maintenance 1-  reproduction maturitybuffer maturation p foodfeces assimilation reserve

A brief history of ‘DEBtox’ The 2000’s …  Péry et al (2002, 2003) modifications for midges  Ducrot et al (2004, 2007) midges and snails  Lopes et al (2005) link to matrix models  Billoir et al (2007, 2008) matrix models, Bayes, new derivation  Muller et al (2010) alternative formulation division

A brief history of ‘DEBtox’ In our group …  Jager et al (2004), Alda Álvarez et al (2005, 2006) multiple endpoints and ageing population (Euler-Lotka)  Baas et al (2007, 2009) mixtures: lethal effects division

A brief history of ‘DEBtox’ Embryo division …  Klok & De Roos (1996), Klok et al (1997, 2007) earthworm matrix model, Bayesian approach

A brief history of ‘DEBtox’ Applying ‘DEB3’ …  Jager et al (2010) basis and mixtures  Jager & Klok (2010) compare methods and population level

A brief history of ‘DEBtox’ New offspring …  E.g., from current PhD projects …

Summary  Toxicants are an integral part of life difference between natural and man-made is a matter of time and spatial scale  For effects on life-history traits, DEB follows naturally food is used to fuel all traits over the life cycle toxicants affect DEB parameters should allow extrapolation to untested conditions  Valuable for environmental risk assessment teasing rules for metabolic organisation out of a living system

Final thought Occam’s razor for dummies …