Lanfax Labs in association with Choice tested 49 powder detergent concentrates in early 2007, resulting in "Wash Only" data for 35 powders in front loaders and 35 powders in top loaders. The report was published in "Choice" in the April edition. The data below extend to dual testing of products where one brand was suitable for both front and top loader.These data are presented independently of "Choice".
Sodium salts are used in laundry products because they are relatively inexpensive and always soluble. Sodium will not form complexes with other components of wastewater to form undesirable products. However, sodium in high concentrations can be detrimental to plants and soil. In plants, the sodium disrupts the osmotic balance (balance between cell water and water outside the cell) and plants suffer from "induced drought". The leaves look like they need a good drink, and in extreme cases the edges of the leaves die off or appear 'burnt'. Many plants are sensitive to even low levels of sodium, while others can tolerate reasonable levels. Many more plants are killed by even small levels of sodium than by other compounds (phosphorus or boron). Sodium chloride (common salt) is an excellent weed killer.
When sodium is introduced into soil, the sodium can cause the soil to disperse, that is, the fine clay particles separate and move into suspension in the soil water. Sodium is, therefore, a good dispersing agent and one of the reasons it is used in laundry products. Soil dispersion leads to a loss of a soil's ability to absorb and move water through the soil pores. Permeability is reduced and when irrigation is applied, a reduced volume of water moves from the surface into the soil profile. Many clay soils can be adversely affected by irrigating with water high in sodium. Sandy soils and sandy loams are unlikely to be affected, but the plants may be affected.
Sodium, therefore, can be detrimental to both plants and soils.
Sodium salts are often used as "manufacturing agents" in laundry detergents, that is, they are use to make manufacturing easier and most of these agents are simply "fillers" that don't change the quality of the wash. Some add to the capacity of the builders but are only of benefit in very hard water.
Sodium may be represented in several ways. As concentration, in milligrams of sodium per litre of wash water, the effect of sodium may be extreme. Dilution is often required to reduce the concentration and that can be done by mixing the wash water with the rinse water. If possible, a preferable choice is to discharge the high sodium water to sewer and use only the rinse water. For those homes on septic tanks, the problem is exacerbated because all the wastewater enters the septic tank where there is some dilution. What then becomes important is the calculated load of sodium that may need to be deposited over the garden or lawn. The load, in grams per wash, is presented in graphs 104A and 104B and the frequency analysis (number of products in each range) of the concentration is presented in 104C.
Interpretation: To interpret the graphs, the shorter the bar the better for soils that may be adversely affected by sodium (clay loams and clays), or plants that are sensitive to sodium. See advice from your horticulturalist is in doubt. As a means of evaluating the potential risk to your soil, you need to estimate the area of garden or lawn over which you intend to spread the wastewater, then calculate the annual load of sodium as a salt load per hectare equivalent. See the calculation below. See previous reference to sandy soils.
Because sodium is very difficult to remove from wastewater, prevention is better than cure. Consider using products that are low in sodium. Note that concentrated powders have a lower sodium level because of the lower use of "fillers".
It is interesting to note that the products specially formulated for front loaders have high levels of sodium as do many of the generic brands. It can be interpreted from this that these products are more environmentally hazardous than those with very short bars.
NOTE: The replacement of sodium salts with potassium salts would result in a wastewater that had a benefit for lawns and gardens rather than the detrimental sodium salts. Potassium salts are also readily soluble in cold water.
Calculation of Sodium per wash
Sodium concentration in the wash water is translated to sodium in the
irrigation area by multiplying the concentration (mg/L) by the volume of water
(L) from the
wash cycle. Front loaders use less water in the wash cycle than top
loaders for the same size of wash - this is may vary considerably across
the various brands and how the washers are used in daily activities.
| Laundry product's sodium load (from graph 104A or 104B) | 20 grams per wash |
| Number of washes per week | 7 |
| Number of washes per year | 365 |
| Sodium load each year (wash load X number of washes per year) | 20 g x 365 = 7300 g = 7.3 kg (1000 g = 1 kg) |
| Area to be irrigation with washing machine water over the whole year | 100 m2 |
| Actual load in kg/ha (sodium load divide by area and multiplied by 10000) | 730 kg/ha |
| Convert sodium load to salt load (divide by 0.4) | 730 / 0.4 = 1825 kg salt per hectare. (See explanation below) |
| Assessment (if salt load greater than 1000, need to increase area) | require at least 180 m2 to safely distribute that load |
Note: A salt load of 1 tonne per hectare is considered in agricultural enterprises to be level at which the productivity of plants decreases, that is, there is a loss of vegetation because of the stresses introduced into the environment around the plant. While this is a simplistic approach, it is one which provides a rough assessment of the quality of irrigation water. The conversion of 0.4 from sodium to salt is to account for the proportion of sodium in sodium chloride.