Conventional bleaching of wood pulp using elemental chlorine produces and releases into the environment large amounts of chlorinated organic compounds , including chlorinated dioxins .  Dioxins are recognized as a persistent environmental pollutant, regulated internationally by the Stockholm Convention on Persistent Organic Pollutants . Dioxins are highly toxic, and health effects on humans include reproductive, developmental, immune and hormonal problems. They are known to be carcinogenic. Over 90% of human exposure is through food, primarily meat, dairy, fish and shellfish, as dioxins accumulate in the food chain in the fatty tissue of animals. 
In second grade spelling, students should be well on their way to mastering sight words and basic phonics. Second grade students are ready for the next level of sight words and more complicated phonetic patterns. VocabularySpellingCity has compiled second grade Dolch and Fry word sight word lists to use during word study and phonics instruction. Sight word lists can be paired with several of VocabularySpellingCity’s games, such as Word-O-Pillar or Splat-N-Spell , to build sight word fluency. Games such as Initial Sound Speller are suitable for phonics practice.