Sediment quality assessment criteria:

new approaches and views

M. Sprovieri, N. Sabatino, M.C. Lombardo, M. Sammartino, D. Valenti

IAS-CNR, Italy (mario.sprovieri@cnr.it) University of Palermo, Italy

11th International SedNet Conference, 3-5 April 2019 Dubrovnik, Croatia

ENVIRONMENTAL RISK ASSESSMENT

Environmental Risk Assessment (ERA), including sediment assessment, is a COMPREHENSIVE approach to support decision making in the regulatory context, and covers a wide spatial set of situations under very different regulatory contexts

MY TODAY’S JOB…

It is a question of interfaces

Where the EqP model coupled to BLM, WHAM and speciation models fail

A quick glance on the complexity of the environment

Ecotoxicology under pressure

Dynamics vs thermodynamics vs kinetics

Proposal of a systemic approach: toxicity as an emergent property

PROCESSES AT THE INTERFACE

A GIANT PROBLEM OF CHEMISTRY AT THE INTERFACES

ECOTOXICOLOGY AND CHEMICAL SPECIATION: A GLANCE AT THE BOUNDARY

THE SEDIMENT PUZZLE

Porewater – Org

Partitioning to pore water

MnO2 – M = POC – Corg FeOOH – M

Binding to sediment phases

Ξ POC – M

H2S/FeS/FeS2 (sulfides)

Porewater – Mn+

Partitioning to pore water

MnO2

Fe3+/Fe(OH)3/FeOOH

Mn2+

FeS + M2+ MS + Fe2+

Reaction with AVS

Oxic

Sub-oxic

Anoxic

SEDIMENT

BIOAVAILABILITY…A CHALLANGE IN ITSELF

Equilibrium Partitioning [EqP] model (Di Toro et al., 2005) for metals Simultaneously Extracted Metals [SEM] (Di Toro et al., 2005) Acid Volatile Sulphide [AVS] Organic Carbon Fe,Mn hydroxide Grain Size

Equilibrium Partitioning [EqP] model (Di Toro et al., 2005) for POPs Grain size Organic Carbon Black carbon Aging

SEM = AVS + FOCKOCCW + Kd(a+b[FeOx+MnOx])

EqP-MODEL FOR METALS

AN OPERATIONAL APPROACH

SEM = AVS + FOCKOCCW

AVS, SEM… DEFINITIONS AT WORK

AVS= FeSmackinawite+FeSgreigite+FeSaquo+FeSclusters + …

FOCKOCCW

Kd(a+b[FeOx+MnOx])

SEM= [Ni]+[Cd]+[Zn]+[Sn]+[Ag]+[Hg]; Ksp>Ksp, Pyrite

FeS and Fe3S4 minerals have rarely been reported from marine sediments

The measurement of AVS-S cannot be related directly to any particular sulfide component in a sediment

Analytical protocols for AVS-S vary considerably and are entirely empirical. Different protocols leach different amount of AVS materials

AVS-S is not equivalent to FeS-S Pore water analyses will include filter-passing,

nanoparticulate solids as well as clusters and complexes Pyrite-S contributes to AVS-S and analytical protocols

cannot be assumed to separate S(-II) components from pyrite-S

The effects of sample handling on measurements of AVS-S have not been quantified

A DEEP GLANCE TO THE AVS PROBLEM

SEM = FeS + FOCKOCCW + Kd(a+b[FeOx+MnOx])

BIOAVAIL. = SEM + Σi fOC Ki,OC FCVi + EXTRA-M

POPs [MeHg] N-SEM EXTRA-M

Sediment Transport

Biotic Ligand Model

Toxicity Production

HydrodinamicTransport

O Carbon Production

Water Effects Ratio

Food Chain

Chemicals Fate and Transport

Biotic Sediments Accumulation

ratio

Ecological Risk Assessment

…BY THE WAY, THE SYSTEM IS COMPLEX AND HIGHLY DYNAMIC

Ecotoxicology (mainly bioassays) under pressure…

An integrated view of processes…no system understanding

A static view of sediments: (thermo)dynamics vs kinetics

A black-box of responses: limited understanding of dynamic chemical processes at the sediment interfaces

Only a “linear” exploration of COMPLEXITY

False positives and negatives obscure/hide complexity

NEED OF A MUCH MORE DEEPER LEARNING

Improved biogeochemistry and system non-linear responses

Dynamics vs Stable conditions

Improved scientific handling of environmental variables

An integrated view of processes

Complexity vs linearity

From a linear and/or combined view of pollutants behaviour, multiple physical parameters of sediments and aquatic/biotic interfaces to… a systemic approach

Analysis of emergent properties of the whole chemical-physical and ecological system rather than of any or a simple addition of its components

COMPLEX SYSTEM AND EMERGENT PROPERTIES

Properties of the system as a whole rather than properties that can be derived from the properties of components of a system

Emergent properties are a consequence of the relationships between system components

They can therefore only be assessed and measured once the components have been integrated into a system

EMERGENT PROPERTIES

Properties of the Whole vs. Properties of the Parts

Sum of the Actions Product of Interactions

BIOAVAILABILITY/TOXICITY EMERGENT PROPERTY OF A COMPLEX SYSTEM

MINERALOGY AND DYNAMICS OF PHYSICAL AND CHEMICAL

PARAMETERS

GEOCHEMISTRY AT WORK

A FIRST EXAMPLE OF AN APPROACH IN TERMS OF A COMPLEX/DYNAMIC SYSTEM

Fe(OH)3 + 3H+ = Fe2+ + 3H2O Fe2+ + ¼ O2 +2OH- + 1/2 H2O = Fe(OH)3 FeS + H2S = FeS2 + H2 FeS2 + H+ = Fe2+ +HS- +S0 FeS2 + 8H2O + 14Fe3+ = 15Fe2+ + 2SO4

2- + 16H+ FeS2 + H2O + 7/2O2 = Fe2+ + 2SO4

2- + 4H+ Fe2+ + HS- = FeSH+ Fe2+ + H2S = FeS + 2H+ FeS + 2 H+ = Fe2+ + H2S FeS +H+ = Fe2+ + HS-

BASIC SYSTEM OF EQUATIONS

BASIC SYSTEM OF EQUATIONS

SO42− + 10H+ ka

−−! H2S+ 4H2O

SO42− + 9H+ kb

−−! HS− + 4H2O

HS− + H+ kc−−! H2S

Fe2+ + 14O2 + 2OH− + 1

2H2O

k1−−! Fe(OH)3

FeS+ H2Sk2

−−! FeS2 + H2

FeS2 + H+ k3 −− Fe2+ + HS− + S0

FeS2 + H2O + 72O2

k4−−! Fe2+ + 2SO4

2− + 4H+

Fe2+ H2Sk5

−−*) −−k− 5

FeS+ 2H+

SO42− + 10H+ ka

−−! H2S+ 4H2O

SO42− + 9H+ kb

−−! HS− + 4H2O

HS− + H+ kc−−! H2S

Fe2+ + 14O2 + 2OH− + 1

2H2O

k1−−! Fe(OH)3

FeS+ H2Sk2

−−! FeS2 + H2

FeS2 + H+ k3 −− Fe2+ + HS− + S0

FeS2 + H2O + 72O2

k4−−! Fe2+ + 2SO4

2− + 4H+

Fe2+ H2Sk5

−−*) −−k− 5

FeS+ 2H+

SO42− + 10H+ ka

−−! H2S+ 4H2O

SO42− + 9H+ kb

−−! HS− + 4H2O

HS− + H+ kc−−! H2S

Fe2+ + 14O2 + 2OH− + 1

2H2O

k1−−! Fe(OH)3

FeS+ H2Sk2

−−! FeS2 + H2

FeS2 + H+ k3 −− Fe2+ + HS− + S0

FeS2 + H2O + 72O2

k4−−! Fe2+ + 2SO4

2− + 4H+

Fe2+ H2Sk5

−−*) −−k− 5

FeS+ 2H+

SO42− + 10H+ ka

−−! H2S+ 4H2O

SO42− + 9H+ kb

−−! HS− + 4H2O

HS− + H+ kc−−! H2S

Fe2+ + 14O2 + 2OH− + 1

2H2O

k1−−! Fe(OH)3

FeS+ H2Sk2

−−! FeS2 + H2

FeS2 + H+ k3 −− Fe2+ + HS− + S0

FeS2 + H2O + 72

O2k4

−−! Fe2+ + 2SO42− + 4H+

Fe2+ H2Sk5

−−*) −−k− 5

FeS+ 2H+

SO42− + 10H+ ka

−−! H2S+ 4H2O

SO42− + 9H+ kb

−−! HS− + 4H2O

HS− + H+ kc−−! H2S

Fe2+ + 14O2 + 2OH− + 1

2H2O

k1−−! Fe(OH)3

FeS+ H2Sk2

−−! FeS2 + H2

FeS2 + H+ k3 −− Fe2+ + HS− + S0

FeS2 + H2O + 72

O2k4

−−! Fe2+ + 2SO42− + 4H+

Fe2+ H2Sk5

−−*) −−k− 5

FeS+ 2H+

SO42− + 10H+ ka

−−! H2S+ 4H2O

SO42− + 9H+ kb

−−! HS− + 4H2O

HS− + H+ kc−−! H2S

Fe2+ + 14

O2 + 2OH− + 12H2O

k1−−! Fe(OH)3

FeS+ H2Sk2

−−! FeS2 + H2

FeS2 + H+ k3 −− Fe2+ + HS− + S0

FeS2 + H2O + 72

O2k4

−−! Fe2+ + 2SO42− + 4H+

Fe2+ H2Sk5

−−*) −−k− 5

FeS+ 2H+

SO42− + 10H+ ka

−−! H2S+ 4H2O

SO42− + 9H+ kb

−−! HS− + 4H2O

HS− + H+ kc−−! H2S

Fe2+ + 14O2 + 2OH− + 1

2H2O

k1−−! Fe(OH)3

FeS+ H2Sk2

−−! FeS2 + H2

FeS2 + H+ k3 −− Fe2+ + HS− + S0

FeS2 + H2O + 72O2

k4−−! Fe2+ + 2SO4

2− + 4H+

Fe2+ H2Sk5

−−*) −−k− 5

FeS+ 2H+

SO42− + 10H+ ka

−−! H2S+ 4H2O

SO42− + 9H+ kb

−−! HS− + 4H2O

HS− + H+ kc−−! H2S

Fe2+ + 14O2 + 2OH− + 1

2H2O

k1−−! Fe(OH)3

FeS+ H2Sk2

−−! FeS2 + H2

FeS2 + H+ k3 −− Fe2+ + HS− + S0

FeS2 + H2O + 72

O2k4

−−! Fe2+ + 2SO42− + 4H+

Fe2+ H2Sk5

−−*) −−k− 5

FeS+ 2H+

1)

3)

4)

5)

8)

2)

6)

7)

k = 1040

k = 1033

k = 107

kcin = 1.5*1013 l2 mol-2 atm-1 min-1

k = 106.1 Kcin = 1.03 * 10-4 l mol-1s-1

Ksp = 10-16.4 Kcin = 1 * 10-7.52 mol m-2 s-1

kcin = 10-10 mol m-2 s-1

K =10– 3.7 kcin= 7 l mol-1 s-1

x1(t) = [F e2+ ] x2(t) = [F eS] x3(t) = [F eS2]

x4(t) = [H2S] x5(t) = [H S− ]

8>>>>>>>>>>>>>>>>>>>>>>>><

>>>>>>>>>>>>>>>>>>>>>>>>:

dx1

dt= C − k1

A

[H + ]2[O2]

1/ 4[H2O]1/ 2x1 + k− 5[H+ ]2x2 + k4[H2O][O2]

7/ 2x3

− k5x1x4 − k3[S0] x1x5,

dx2

dt= − k2x2x4 + k5x1x4 − k− 5[H

+ ]2 x2

dx3

dt= k2x2x4 + k3[S

0] x1x5 − k4[H2O][O2]7/ 2 x3

dx4

dt= − k2x2x4 − k5x1x4 + k− 5[H

+ ]2 x2 + kc[H+ ] x5 + ka[SO2−

4 ] [H + ]10

dx5

dt= − k3[S

0] x1x5 − kc[H+ ] x5 + kb[H

+ ]9 [SO2−4 ]

DYNAMICAL

SYSTEM

Non-linear system, continuous and converging towards attractors. System stable at various conditions

Trajectories of the different species in the Eh-pH stability field are well-described and quantified

We can calculate the buffer (complexing) capacity of the FexSy system

Need of field-tests to verify theory

SPECIFIC FEATURES OF THE SYSTEM

Eh(V

) [FexSy] (mmol)

Av. Metals

1x10-3 3x10-3 2x10-3 5x10-3 4x10-3 0 8x10-3 6x10-3 7x10-3

FEXSY NORMALIZATION

SEDIMENT AVAILABLE CADMIUM (mmol/mmol FeS)

MO

RTA

LITY

(%

)

Eh=-0,5V Eh=-0,2V

…MY TAKE HOME MESSAGE… We must re-think our approach to evaluation of

sediments bioavailability/toxicity in terms of complex system and biogeochemical dynamics. Non linear addition of “pieces” but approaches to emergent properties

Eh, pH, O2 (physics) dominate dynamics of [Fe, S, OC,FE/Mn hydroxides] chemistry in sediments: we need new and more “conservative” sampling methods

Dynamics dominate stable conditions…this is complexity at work

Ecotoxicity needs a deeper understanding of biogeochemical dynamics of pollutants in seds

Thanks for your attention!