Seawater has an extremely complex chemistry, however a relatively few constituents make up the bulk of the components. The pie chart and table below present the main components.

Most abundant solutes in seawater

Constituents

(Ions)

Concentration

g/kg

Weight Percent

(%)

Chloride (Cl-) 18 .9799 1.9
Sodium (Na+) 10.5561 1.1
Sulphate (SO42-) 2.6486 0.3
Magnesium (Mg2+) 1.2720 0.1
Calcium (Ca2+) 0.4001 0.04
Potassium (K+) 0.3800 0.04
Bicarbonate (HCO3-) 0.1397 0.01
Bromide (Br-) 0.0646 0.0065
Trace Elements 0.633 0.1
total 35g/kg 3.5%

 

Chemical Parameter Typical seawater Units  
Cation metals
Potassium K 380 mg/l
Sodium Na 10.5 g/l
Calcium Ca 400 mg/l
total hardenss Ca & Mg 6600 mg/l
Strontium 8 mg/l
Arsenic 3 ug/l
Magnesium Mg 2 g/l
Aluminium Al 0.5 ug/l
Lead Pd 0.002 to 0.03 ug/l Helmers 1996 N & S Atlantic, Bermuda 0.016 ug/l Boyle et al 1994
Iron Fe 10 ug/l
Mercury Hg 0.05 ug/l
Manganese Mn 2 ug/l
Copper Cu 2.0 ug/l
Nickel 0.5 ug/l
tin 3 ug/l
Zinc 7 ug/l
Cadmium 0.03 ug/l
Chromium 10 ug/l
Selenium 0.2 ug/l
Anions
Alkalinity as CaCo3 140 mg/l
Chloride 18.9 g/l
Sulphate 2.4 g/l
Total phosphorous 0.07 mg/l
Dissolved phosphorous mg/l
Organic phosphate mg/l
Cyanide ug/l
Non metallic
boron 4.8 mg/l
Silica free mg/l
Silica total 3 mg/l
Dissolved gases
CO2 ( carbon dioxide) <10 mg/l mg/l5
O2 ( dissolved oxygen) 6 to 10mg/l mg/l5
N2 nitrogen partial pressure <100 %sat5
Organics
COD (chemical oxidation demand) <2 mg/l mg/l
BOD (biochemical oxidation demand) < 1 mg/l mg/l
TOC ( total organic carbon) 0.1mg/l min range <1 mg/l mg/l
DOC ( dissolved organic carbon, 0.1mg/l min range <0.05 mg/l ug/l
Physical parameters
pH 8.0 to 8.3 pH
ORP ( redox) 250 to 350mv mv
Pt-Co Colour <1 mg/l Pt
Turbidity <0.1 NTU
Suspended solids < 1 mg/l
TDS (total dissolved solids) 35 g/l
conductivity mS
Halogens
Chlorine mg/l
Bromine 65 mg/l
Iodine 0.05 mg/l
Fluoride 1.3 mg/l
Nitrogen
Ammonium-N, 0.1 mg/l
Nitrite-N mg/l
Nitrate-N mg/l
List 1 chemicals
Total pesticides ug/l
TBT (tributyltin) ug/l
Pesticides (total) ug/l
PAHs (Polyaromatic hydrocarbons) ug/l
PCB1s ( polychlorinated biphenols) ug/l
phenol ug/l
Bacteriological 
total coliform < 10 per 100 ml
faecal coliform <1 per 100ml
Total bacterial level at 22 deg C per ml
Total bacterial level @ 37 deg C per ml

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