Sodium
The effects of salinity cover the general ionised components of the laundry water (cations and anions of all the salts) that together can affect the normal functioning of plants (by upsetting their water balance), change the availability of other plant nutrients (nutrient imbalance) or lead to a hostile soil environment with changed structural stability. However, some salts are beneficial and are used as a remedy to overcome soil problems. Heavy clay soils can be ameliorated with lime or dolomite (also increases pH) or gypsum (no change to pH), but these products significantly change the soil salinity status. Fortunately, the majority of the cations are calcium or magnesium and these elements are essential plant nutrients.
Unfortunately for laundry product manufacturers, sodium salts have the best and the worst characteristics. All sodium salts are highly soluble, hence of a benefit when manufacturers want to get their products rapidly dissolved in cold water. Sodium (as the cation) is used in various combinations with anions to form highly soluble salts. Phosphorus is often carried as sodium tripolyphosphate, the sodium part making it highly soluble. Washing soda is sodium carbonate, a highly soluble, yet highly alkaline product.
Secondly, because sodium can be detrimental to plant physiology (affect osmotic pressure in plant cells) and lead to loss of soil structure, the amount of sodium in laundry detergents needs to be limited when the wastewater is to be discharge to vegetation or soil absorption areas. When wastewater is discharged as "ocean outfall' (the dark ages approach to sewage disposal) the sodium concentration is irrelevant, but the loss of phosphorus to the oceans is a waste of a limited resource (environmental vandalism).
The detergents were again mixed at the rate for front loaders and top loaders and the concentration of sodium determined by ICP, along with other elements.
Since the only guide to the 'desirable' upper limit of sodium is based upon loss of plant production, an other term "sodium adsorption ratio" is in common use. This term, when stated simply is a measure of the proportion of sodium relative to beneficial elements calcium and magnesium (the ratio is complex and beyond the scope of this section). It is well know that sodium adsorption ratios (SAR) above 5 can have a significant negative influence on soil structural stability, most of the laundry detergents have significantly higher SARs for two reasons; one is that they have very high sodium levels; and, secondly because they have very low calcium and/or magnesium levels (these two elements give rise to 'hard' water). It is not desirable that the SAR be stated for these products because the contribution of dirty clothes and town water supplies may change the concentration of calcium and magnesium in the wash water. The detergents have the task of isolating the calcium and magnesium salts and removing them before they can precipitate into the fabric of the clothes.
What we need to consider is the level of sodium in the laundry product. The lower is better in this case. As a guide, I consider 200 mg/L of sodium as a cut-off level (although I prefer lower levels depending upon soil type). Sodium concentrations above this are more than likely to have a negative impact on plants and soil, however, some plants are so sensitive to sodium that even very low levels may be detrimental. One needs to consider the plant type and soil properties to accurately assess the potential impact of sodium on the environment.
Figure F3 - Na Sodium concentrations when the recommended dose of detergent is mixed in 75 L full wash for a front loader
Figure T3 - Na Sodium concentrations when the recommended dose of detergent is mixed in 150 L full wash for a top loader
Assessment
The assessment of laundry detergents based upon the sodium concentration is one which has not been addressed by the product manufacturers themselves, or the industry regulators, or the municipal sewage treatment plant operators. It is clear that whatever the manufacturers want to make, however they market their products and how they are used in homes across the world is something that we should just accept as driven by market forces. It is here that I am in absolute disagreement. I consider many of the products listed above should be removed from sale as they have the potential to seriously degrade our land environment. Sodium in large concentrations is detrimental to plants and soil. Simple demonstrations can show the effect of laundry detergents on a range of soil - results visible in a couple of hours, do not have to wait years for the actions to be clearly seen.
If the 'desirable upper limit' of 200 mg/L (this must include sodium from the source water), then 53% of the front loading detergents are above this limit and 34% of top loading detergents exceed this value. The greater volume of water from the top loaders give the ability to spread the load of sodium (g/wash) over a greater area. One is limited by the smaller volume of water in front loaders and distributing the sodium load over a large area becomes difficult (mostly likely not done).
The solution is simple. Test out a small section of your garden or lawn to see what happens when you discharge laundry water. Check on the condition of the plants (do they look healthy?) and see what happens to the soil. You can check to see what the soil looks like when you dig up a small section - if it looks to be clumping together - you may have a problem. If the surface looks like its covered with a fine sheet of clays, you again have problems.