Metallic species tend to adsorb to organic matter found in the sedimentary phase. In particular, microbial biomass and its associated exopolymeric matrix could be important sites for metal capture.

How are you digesting the sediment samples?

I would assume that some of the metals are actually in the sediments themselves such that they come out of the sediments during the digestion

There is several publications on this topic, buy most of it is adressed to freshwater systems and wetland watewater treatment. I don't have the exact bibliography at hand, but you can search "ecological engineering" papers (Elsevier).

In the case of wetland treatment, there is a clear acumulation of HM on plant tissues (not homogeniously, most in the extracelular space) and in the sediments, maximum at root proximity. It seems this effect is due to the water plants hability to modify pH in his near rizosphere in order to "control" the compounds that enter.

Hope it helps you...

Thank you very much. Your replies have been useful.

Dear Reema

Can you be more precise on your question? Are you comparing concentrations in µg/g in sediment with µg/l in water ? (a thing that you cannot do) And which water is it, porewater or water from the above water column ?

Dear Reema,

I agree with Olivier as you should compare the same range of concentrations and else I agree with Otto as in sediment the metallic compounds often adhere with sediment particle and depend highly in granulometry of particle and so nature (sandy, clay or others).

The answer to you question is that it is a matter of thermodynamics. Given sufficient time the system will tend to its equilibrium position in which the Gibbs free energy of the system will be minimised. Depending on the conditions, the metals may tend to be sorbed on the sediment, precipitated as oxides, phosphates, sulphides or sulphates etc. or be apparently present as free ions in the water (but in fact may be present as complexes or colloids). The other thing to remember is that this is not fixed in time and as conditions change, particularly oxidation states, the distribution may change. It may be found that, in rapidly changing environment such as an intertidal situation, the distribution that you observe is as much dependent on kinetics as it is on what might be achieved at equilibrium. Actually it is some time since I have worked in this area but in the past I have found that literature on soil and agricultural chemistry can give a lot of useful insight into this. You may wish to search in this area too.

Dear Reema

I suggested some bibliography which can answer your question:

Barra et al 2001. Chemosphere 45: 749-757

Bollmohr et al 2007. Chemosphere 68: 479-488

Carriquiry and Sanchez 1999. Marine Geology 158: 125-145

Daesslé et al 2004. Continental Shelf Research 24: 2093-2106

De la Cal et al 2008. Chemosphere 70: 1182-1189

García-Hernández et al 2001. Journal of Arid Environments 49: 65-89

Hung Minh et al 2007. Archives of Environmental Contamination and Toxicology 52: 458-465

Santschi et al 2001. Marine Environmental Research 52: 52-79

Shumilin et al 2002. Marine Chemistry 79: 113-131

Valette-Silver, NJ. 1993. Estuaries 18: 577-588

Long and Morgan 1990. NOAA Technical Memorandum NOS OMA 52

I hope there are ussefull to you

Dear Reema

Just to add to the erudite answers you have received already. We have previously measured metals in (fresh) water and sediments and correlated these with biological responses (biomarkers) in fish, as well as standard physical chemical aspects of water quality.

In the paper (Gill damage, metallothionein gene expression and metal accumulation in Tilapia sparrmanii from selected field sites at Rustenburg and Potchefstroom, South Africa. Daléne Van Heerden, Peet Jansen Van Rensburg, Mikko Nikinmaa, André Vosloo. African Journal of Aquatic Science 01/2006; 31(1):89-98.) we drew an ordination diagram (Fig. 2) to assist in data reduction, and the trends were very much what you would expect from text books: partitioning into the water column was favored by increased temperature, increased conductivity and decreased pH. The ordination also allowed us to demonstrate that gill metallothionein levels correspond to water metal levels (short-term response), whereas liver metallothionein levels reflect sediment metal levels (long-term response).

I suspect in the highly variable estuarine environment these trends would be even more apparent. Just make sure you have sufficient paired water and sediment samples (also biologicals) from each of your sites.

Kind regards

PS if you can't get the paper from RG, please send me a message through my RG page

..this paper should give you some insight into the answers you seek

..and this too. Cheers

Article Spatial and Temporal Variations in Water and Sediment Qualit...

Try the following paper: "The origin of speciation; trace metal kinetics over natural water-sediment interfaces and the consequences for bioaccumulation". You'll find metal profiles over redox zones.

Jos.P.M. Vink (2009). Environ. Poll. 157:519-527.

The sediment sample was collected from the intertidal region of a beach and digested using nitric acid and perchloric acid. The metals tested for were Zn, Cr, Cu, Fe, Ni and Pb from both sediment and surface water. Is the permissible limit same for both open water and coastal water? Can the permissible limit for fresh water be used for marine sample?

..permissible limits for freshwater are not applicable to marine samples because the circumstances of metal toxicity for the two environments are different.

Hi, I'm Isidore, Doctor of Biological Sciences, you can check the items that I have published, I think I can help.

regards

You could try to go through a "sequential extraction" of the sediment rather than digesting the sample directly ...you can find the heavy metal concn. distribution as : exchangeable fraction, organic fraction, ...residual fraction, so on and so forth....

You can use EDTA....or such metal complexing reagents (sorry I don't remember exactly). May be then you can correlate with the concentration for the same in the water sample. Of course pH will be an important factor.

You can just type in: "Sequential extraction of heavy metals in sediments/soils" in google and get many literature.

The associations of many metals with the organic carbon content of sediments and other oxide phases (iron and manganese) are very important in the distributions of metals between water and sediments. pH is a large driver in solubility of metals as well

Be careful with the units you are using for this comparison. Water concentrations are in mg/l (of water) or ppm, and in sediments mg/g of sediment therefore units not comparable.

in general, distribution of heavy metal "or any chemical compound" between soil (or sediments) and water phase is defined by sorption isotherm studies. You will find Freundlich distribution coefficient where the largest value implies stronger sorption on sediments. Also, Langmuir parameters where the maximum sorption capacity is a very useful indicator of the heavy metals retention on soils or sediments.

We have carried out a lot of work on Metal Concentration in Water and Sediment of river Hindon, India. You can go through some of our published paper Jain and Sharma. It will help you.

It's hard to know more without knowing something about the characteristics of the sediments (terrigenous vs oceanic in origin), but two factors are likely at play here:

1) If the sediments are derived from crustal erosion, the metals you are seeing are likely naturally occurring and it makes complete sense that the sediment concentrations are higher than the water (also, as someone else mentioned, be careful about unit conversions here).

2) If the origin of the sediments are something other than crustal erosion (e.g. biological CaCO3), then it's still possible that the sediment would be higher than the water. How frequently did you measure the water? Water concentrations can vary over short periods of time (minutes to hours), whereas sediment concentrations tend to be much more stable (months to years depending on the system). So in other words, even if the water column is a source of the metals and the sediments are a sink, it's easy to "miss" high concentration events in the water column.

check out some of the following papers ...

Acid volatile sulfide predicts the acute toxicity of cadmium and nickel in sediments

DM Di Toro, JD Mahony, DJ Hansen… - Environmental …, 1992 - ACS Publications

Predicting the toxicity of metal‐spiked laboratory sediments using acid‐volatile sulfide and interstitial water normalizations

…, JD Mahony, DL Robson, DM Di Toro… - Environmental …, 1996 - Wiley Online Library

Technical basis and proposal for deriving sediment quality criteria for metals

GT Ankley, DM Di Toro, DJ Hansen… - Environmental …, 1996 - Wiley Online Library

A model of the oxidation of iron and cadmium sulfide in sediments

DM Di Toro, JD Mahony, DJ Hansen… - Environmental …, 1996 - Wiley Online Library

check out this paper

Alicia Rendina & Alicia Fabrizio de Iorio (2012): Heavy Metal Partitioning in

Bottom Sediments of the Matanza-Riachuelo River and Main Tributary Streams, Soil and Sediment

Contamination: An International Journal, 21:1, 62-81

and some of my works in organic matter and metals in river sediments of the Matanza river (abstract on my profile)

Our group study river sediments and water.

you should focus role of DIC, pH, Oxygen, Silfide , grain size, TOM, Redox condition, in distribution of heavy metal in sediment and water. bioavailability is another important parameter in distribution of heavy metals.

Heavy metals have more than 5 g/cm3 density. Therefore, they always sink spontaneously in the water column or with very small particles by absorbing/holding. And also there are too many literature about the heavy metal sources, accumulations and/or pollutions in the sediment. I think you should more careful to search criterias. I am studying about it.

Most sediments are sinks for trace/heavy metals, and there are many factors that affect how much of a difference will exist between the water and the sediment.

These include as most before have listed factors such as carbon content, mineralogy, sulphide production, redox, but also sediment mineral crystallinity, surface site density, reactive surface areas, etc. All affect the partitioning between the water and the sediment and is measured by the partition coefficient (Kd). The greater the Kd value the greater the sediment will draw metals out of the the water; a Kd of 1 means that the water and the sediment are equally distributed, however most sediments have Kd values >1000, where there are 3 orders of magnitude difference between the water and the sediment. Hence the water concentration may be 2 µg/L, but the sediment has 2 mg/kg.

The difference between heavy metals concentrations in water and sediments is logic because the sediments is the source (as the upper crustal area) and the main storage area of the natural heavy metals and you can check its natural values in literatures. About the heavy metals in polluted area, also all the colloidal forms finally will settle to the bottom, so it is logic to find sediments has higher concentrations. About the limits, check this reference: USEPA (1997) An SAB report: Review of the Agency's draft ecological risk assessment guidelines. Science Advisory Board United States Environmental Protection Agency, Washington, DC.EPA-SAB-EPEC-97-002.

I am agree with Hazel fulckner. it is not true to compare them. because the units are diffrent. but my researches show that: may be a polluted water is go through sediment for a long time so sediment is polluted. after that may be a clean water come. and this is the time you take samples. water is clean but sediment is polluted. this is the case we examin in Iran. the irrigation water was clean the time we took samples. but soil was polluted. when we aske we understood that befor that time the water was very polluted

Most metals are insoluble in water but bound to sediments, this is the main reason your results with sediments were higher. Furthermore, the metals in the aquatic ecosystems are mainly deposited in sediment, and sediment acts as a source and as a sink. As a consequence, benthic biota living in metal polluted environment can have very high level of metals (note: benthos organisms such as mussels are used in bio- monitoring of heavy metal pollution in marine environment). It is also important to know which metals you have monitored and analyzed for as some metals are more toxic than the others. I hope the permissible range means guideline values you are referring to?

-Some heavy metal guideline values for the protection of aquatic ecosystems in marine environment are as follows: Cadmium (Cd) 0.7 µg/L (99% species protection); Copper (Cu): 1.3 µg/L (95% species protection), lead (Pb): 4.4 µg/L (95% species protection) and mercury (inorganic): 0.1 µg/L (99% species protection)

- some guideline values for sediments: Cadmium (Cd) 1.5-10 mg/kg; Copper (Cu): 65-270 mg/kg, lead (Pb): 50-220 mg/kg and mercury: 0.15-1 mg/kg (low-high trigger values)

What units are you using for your comparison? Sediment concentrations are in mg/ gm or gm/gm of sampled sediment, whereas in water in we obviously use ppm or mg/ l, so for comparative purposes there is clearly an immediate difficulty, as the differing units do not allow you to argue that one 'concentration' is 'higher' than the other., one being in sediment and the other being I water.

I have work on microbiology as Total Count and Vibrio which collected from surface sediment of 4 creek in south of Iran and the result shows the higher density in sediment then water approximately more then 100 time comparing sediment with water in intertidal area

Heavy metals are more in sediments than in water. In water,the sediments come from mineral-water interaction process in which processes like disintegration, dissociation,dissolution are main.Justify the question geological strata, type of mineral and source of water is also important.

Heavy metals are more in sediments because to the sediment play the major role as a sink to this metals in aquatic systems

We did extensive work on speciation of metals over water-sediment interfaces. Try the following two papers:

Vink, JPM (2002) Measurement of Heavy Metal Speciation over Redox Gradients in Natural Water-Sediment Interfaces and Implications for Uptake by Benthic Organisms. Environ. Sci. Technol. 36:5130-5138

Vink, JPM (2009) The Origin of Speciation: Trace Metal Kinetics over Natural Water / Sediment Interfaces and the Consequences for Bioaccumulation. Environ. Poll. 157:519-527

OK, here's the paper on water-sediment speciation. There's much more.

Sediment in the water bodies is derived from a diverse group of sources such as atmospheric inputs, fluvial, continental shelf, biological activity, and erosion of estuarine margins. Sediments possess high affinity for the storage of metals. In hydrological cycle far less than 1% of metals are found dissolved in the water column; more than 99% are stored in the sedimentary environment. Once metals enter the aquatic system, they may get combine to suspended matter, and thus, through sedimentation, they reach the sedimentary environment. Toxic metal content in aquatic system mostly influenced by factors such as sediment texture, mineralogical composition and physical transport .

I had the same problem. In our case heavy metals were deposited in the sediments and represented the 'historical pollution'. They were deposited during the period of the intensive industrial activity. At present time, after the significant reduction of the industrial wastewaters and run-off discharges, the sediments are still enriched in heavy metals, but the surface water shows the low level of the contamination. You can see in Vystavna et al. 2012 and Vystavna et al. 2013 publications, if you are interesting in it.

Sediments are important sinks for various pollutants such as heavy metals and also play a useful role in the assessment of metals contamination . Sediments, particularly surficial sediments, may serve as a metal pool that can release metals to the overlaying water via natural anthropogenic processes, causing potential adverse health effects to the ecosystem because of their serious toxicity and persistence.

The reason for the difference in concentration of metals in water and sediment is because sediment serve as a sink. The metals have accumulated over the years. To the best of my knowledge, there is standard for heavy metals in water and sediment in marine environment.

A full understanding would require a measurement of the forms of the metals. different forms have different solubilities. Heavy metals are often measured by a destructive method (like AA) that only reports on the element: PB, As, Cr, Ba --rather than the substances as they are present in the media: PbS vs Pb(C2H3O2)2 or BaSO4 vs BaCl2 or CrS vs Cr2S3 vs CrCl3.... Here I list the less soluble forms first (but their are many forms). The ratio of a metal concentration in sediment vs in solution gives you insight into the forms that might be present.

Article IMPACTS OF HUMAN ACTIVITIES ON WATER EROSION AND POLLUTION O...

I studied the fluxes between sediment and water in heavy metal in very polluted river sediments. Redox conditions and dissolved organic matter have a very important role

The reducing environment ( Water Logging etc)increases the metal concentration in water.

Sediments have particles (organic matter and minerals) in a size so small (fine grained,

Metal sulfides áre very important in a reducing environment They fixed metals in the Solíd phase. Sediments act like sink when there are sulfides (as FeS)

The equlibrium between different oxidation types in metals could be explain by Free energy of Gibbs. Another variables as pH, oxygen, salinity and sediment size, and also organic matters in sediments and water could be help you to understand the chemistry inside the system. Not all the oxydation types in metals are toxics. Evaluation of toxic levels of metals in organism and food depending in each country, stablishing levels is a hard goal between scientific and goverments. There are many bibliography in Science Direct for example, on pore water and metals, but not all are free access, please ask in your institution or in a library if you have free access. One reference the Environmental Protection Agency (EPA) in USA, but the European community also have their own protocols for heavy metals. Maybe in your country have more information.

Sediments are sinks for most heavy metals and other pollutants. And depending on the metal and it's ability to remain soluble or insoluble in the water. We can't be metal specific or generalize that one holds more than the other but in quite a number of cases, the sediment does.

Heavy metals are hydrophobic and they tend to adsorb to solid materials. they have a positive charge. and clay minerals have negative charge therefore they tend to adsorb it. there are several researches which have similar results with you. if you like I can send some of the references about this subject. that is why sediments plays an important role in pollutant transport.

Metal oxidation state (based on environmental conditions) plays major role in in solubility of metal in water or adsorption on sediments. Like iron, arsenic in reducing environment are soluble in water while oxidising environment make it adsorbed on sediments.

I know that in the point of connection of the river to the sea, due to changes in salinity and other parameters, heavy metals dissolved in river water are flocculated and deposited. Therefore, changes in a some parameters in the river cause heavy metals to flocculate. You can search "flocculation heavy metals" keyword and follow Dr. Karbassi's articles. A. R. Karbassi

https://scholar.google.com/citations?user=nPCS-10AAAAJ&hl=en&oi=ao

Physicochemical characteristics of water affect the precipitation of metals in sediment and metal ions transfer from water to sediment.

Metals in aquatic environments are usually bound to suspended particles or adsorbed to particulate organic matter, which finally settle and accumulate in bottom sediments. Therefore, metal concentrations are higher in sediment and usually exceed those of the overlying water by 3–5 orders of magnitude.

Heavy metals are insoluble in alkaline media such as seawater. They form complexes that precipitate and remain in the sediment

because the heavy metal are in the insoluble chemical forms, so they are suspended in the sedimets or form complexes or precipitate depending of the pH

With respect to “permissible levels” it is common practice in a number of countries to use the Dutch List. see - http://esdat.net/Environmental%20Standards/Dutch/annexS_I2000Dutch%20Environmental%20Standards.pdf

ASEAN has a set of standards for water quality as does ANZAC and both of these are used in the IndoPacific and asian countries

I had some work before your work in the inter tidal area of some mangrove creek some stations were in pollution area and some of them not near city or industrial in Golf of Oman and Persian Gulf in the area of low tide of all stations show higher than High tide area which mean all the pollution come from sea to inter tidal area.

No industrial effluent directly discharge to creek

Irecommned you to analysis bioaccumulation of heavy metals in benthos organism to complete the work and would be easy for you to find the correct answer for your question.

Interdital (anterior shore) microorganism diversity and the presence of a sediment zone for outdoor pollution can be considered

Mine is a question! Is it possible for heavy metal to be present in water but not in the sediment from that area?

It is depend on the source, if it is natural or anthropogenic. The anthropogenic (man made) play important role for increase the pollution from heavy metals in water and at the sink area (sediments). Sediment transportation also is important factor especially at the estuaries and the drains outlets.

It is highly unlikely that any (heavy) metal is present in surface water but not in underlying sediment, simply because of dictating partitioning coefficients. Exeptions may exist in dynamic waters, where metal sources are of distant origin, and/or when dissolved organic carbon (DOC) is high, and reactive.

try this

Article Determination of persistent organic pollutants in water of n...

Article Determination of persistent organic pollutants in water of n...

Article DETERMINATION OF PERSISTENT ORGANIC POLLUTANTS IN WATER OF N...