Effects on Plants

• The tolerance of plants, with regard to chloride concentrations in soils and irrigation water, varies by species. Chlorine deficiencies occur in plants when soil levels drop to 2 ppm, and most topsoils are naturally around 10 ppm. When the tolerance threshold is met, excessive uptake of chloride ions by roots into the plant causes a disruption of photo-reactions in photosynthesis. Chloride acts as a salt, destabilizing the flow or availability of water to plant cells in vascular tissues. Excessive chloride dehydrates plants -- disrupting osmosis -- and can inhibit the utilization of other key nutrient ions in plant fluids.
  
  

Analysis

• The optimal level of chloride in soils and plant tissues is neither universally known nor understood. With no optimal value to use for comparison in experiments, scientists have few other factors to measure and evaluate for a better understanding of chloride levels. Typically, plants can tolerate high concentrations of chloride in the soil without harm, as high as 20,000 parts per million. Dried tissues from healthy plants can reveal internal concentrations of 70 to 100 ppm.
  
  

Swimming Pools

• Although chloride ions act as a salt, when chlorine gas is mixed with water, a salty solution is not the simple result. The vast majority of plants are not harmed by a splashing of swimming pool water due to chloride ions. Instead, the hydrochloric and hypochlorous acids in pool water can scald or burn plant tissues, causing leaf yellowing, wilting or plant decline. These acids naturally and quickly form when chlorine gas comes in contact with the hydrogen and oxygen atoms of water molecules.
  
  

Other Insight

• Chloride ions readily move through soil because they are water-soluble. A soil naturally rich in chloride leaches ions as rainwater trickles downward. Areas of the United States with naturally alkaline soils, which often have soils abundant with chloride, have groundwater that is a salty brine. Irrigating with saline water can negatively affect crops once the chloride tolerance threshold is passed for that particular plant species. However, the negative effects seen on plants are often the cumulative effect of other salt molecules present in irrigation water. While elevated chloride concentrations exist, an increase in sodium, potassium, sulfur or other atoms of dissolved molecules may be equally responsible for growth disruption in plants.