The overall ratings of four chemicals stocks are down on Portfolio Grader this week. Each of these rates a “D” (“sell”) or “F” overall (“strong sell”).

This week, The Mosaic Company (MOS) falls to a D (“sell”), worse than last week’s grade of C (“hold”). Mosaic produces and distributes crop nutrients to the agricultural communities located in North America and other countries. For Portfolio Grader’s specific subcategory of Sales Growth, MOS also gets an F. For more information, get Portfolio Grader’s complete analysis of MOS stock.

Intrepid Potash, Inc. (IPI) earns an F (“strong sell”) this week, moving down from last week’s grade of D (“sell”). Intrepid Potash mines and markets potash for use as a fertilizer. The stock gets F’s in Earnings Revisions and Cash Flow. As of Dec. 6, 2013, 17.2% of outstanding Intrepid Potash, Inc. shares were held short. The trailing PE Ratio for the stock is 27.40. For a full analysis of IPI stock, visit Portfolio Grader.

This is a rough week for Olin Corporation (OLN). The company’s rating falls to D from the previous week’s C. Olin Corporation manufactures and sells chlorine, caustic soda, sodium hydrosulfite, hydrochloric acid, hydrogen, sodium chlorate, bleach products, and potassium hydroxide. As of Dec. 6, 2013, 18.3% of outstanding Olin Corporation shares were held short. To get an in-depth look at OLN, get Portfolio Grader’s complete analysis of OLN stock.

Arabian American Development Company’s (ARSD) rating weakens this week, dropping to a D versus last week’s C. Arabian American Development owns and operates a petrochemical facility located in southeast Texas, which specializes in high purity petrochemical solvents and other solvent type manufacturing. The stock gets F’s in Earnings Momentum, Earnings Surprise and Sales Growth. For a full analysis of ARSD stock, visit Portfolio Grader.

Louis Navellier’s proprietary Portfolio Grader stock ranking system assesses roughly 5,000 companies every week based on a number of fundamental and quantitative measures. Stocks are given a letter grade based on their results — with A being “strong buy,” and F being “strong sell.” Explore the tool here.